I have two things of interest here, in the realm of Minecraft.
I have been maintaining Minecraft X-Ray since December 2010, after that project had been abandoned by its original creator. The utility has changed quite a bit over time, though it still has the same purpose.
I have a table of version information for various versions of Minecraft. When new versions of Minecraft get released, there's often a period of tumult in the community as servers and clients get mismatched versions (often leading to people being shut out of the SMP servers they frequent), and some understandable complaints about new bugs that sneak their way into the versions as well. This often leads to people looking for old versions of minecraft.jar so that they can remain on a previous version until some of those issues are dealt with.
Official Mojang policy is that redistribution of Minecraft is not permitted, so you won't find any Minecraft code here, but it always struck me as an act of faith that people would trust software handed out by strangers on IRC and the like. I felt that it might be useful to keep a table of known versions, with the md5sums and sha1sums that I had on my system for those versions. Hopefully Google will pick this up, and perhaps somebody else on the internet will publish their own list of checksums, and so on. If you do get a version of minecraft.jar or minecraft_server.jar from someone, you might have a few resources to check to see if you have a legit copy or not.
Note that there has been at least one instance where Notch has released a change to Minecraft without actually bumping up the version number, so be careful about that. Also note that obviously this list isn't exhaustive; I didn't start getting thorough about my Minecraft backups until somewhat recently.
MinecraftClientMinecraft Weekly BuildServer
Version Timestamp minecraft.jar md5sum minecraft.jar sha1sum 1.0-rc2 (good version) n/a bd569d20dd3dd898ff4371af9bbe14e1 6e54fbe19b7797f3e3a2cb9feb5da41a40926db8 1.0.0 1321653290000 3820d222b95d0b8c520d9596a756a6e6 b679fea27f2284836202e9365e13a82552092e5d 1.1.0 1326382442000 e92302d2acdba7c97e0d8df1e10d2006 f690d4136b0026d452163538495b9b0e8513d718
Version minecraft_server.jar md5sum minecraft_server.jar sha1sum 1.0-rc2 (good version) c9638ebcfe496a072d3d71c3a131e3d5 8ede92b8efc8ed53dbf3faa2c3a094df8e708509 1.0.0 5ce6f071a62801eb143cddfef5c03160 38cafa1bf1e927c5cdb4cfb8cc6a34dfdcfab2b8 1.0.1 934b6010999daa1f1b1ccdf4cb77e052 ecf944fcef1a630f95ded840de0059d4922f81c2 1.1.0 b0f4fb91f9723104adf35944bbf3d3cf 3dbadea4e8a0923ac5fde9f4b9e98a244ea2589a ClientMinecraft BetaServer
Version Timestamp minecraft.jar md5sum minecraft.jar sha1sum weekly-11w47a n/a 2ad75c809570663ec561ca707983a45b 4e327918708d22e7443fbadefb9831ca04af4b90 weekly-11w48a n/a cd86517284d62a0854234ae12abd019c fede770abe88a19e844d99dda611a7d18184155a weekly-11w49a n/a a1f7969b6b546c492fecabfcb8e8525a 6f92a726e6b8b64f66c7e4d236f983c278d5af54 weekly-11w50a n/a 8763eb2747d57e2958295bbd06e764b1 f4981ba0fee00a16d8dc9ec87bf2c4fdb51e4b7c weekly-12w01a n/a 468f1b4022eb81d5ca2f316e24a7ffe5 653a9cf55884b6bc4dcf3c574331e04bd5ad1032 weekly-12w03a n/a ea85d9c4058ba9e47d8130bd1bff8be9 e581c7c9dd57cbf73f72b833be5eff6109187df0 weekly-12w04a n/a c2e2d8c38288ac122001f2ed11c4d83a 4911c473e856ec8102b8419eb36d0f54dad029a0 weekly-12w05a (second attempt) n/a feabb7967bd528a9f3309a2d660d555d 28328e67b82564335aa8280095a0716a2eb790de weekly-12w05b n/a 70affb4ae7da7e8b24f1bbbcbe58cf0f 75fbc4a39a244d0f1eb842ff8385e992e2b47dd5 weekly-12w06a n/a 9cfaa4adec02642574ffb7c23a084d74 a8403c0d4c0cdb65722d864d9cf42663b8aab08b weekly-12w07a n/a d60621a26a64f3bda2849c32da6765c6 e7ad115b29612b893972f0817030d993bc56fb7e weekly-12w07b n/a 88a9a9055d0d1d17b1c797e280508d83 0eea35d588fc2cee5d397472aa3565f48c220217
Version minecraft_server.jar md5sum minecraft_server.jar sha1sum weekly-11w47a e0f2fa582148d607774a0b81c232fee3 62e447c26123d890fa0bd8fad58b1c3a50c5c4ba weekly-11w48a d0a249287e32edd8d69c62cbd754abf3 75a7953e3dea006503a5ac6d51823a6dc687f6b5 weekly-11w49a 3e1caabf85161b3ef002138d7540401f 36350a3917f63766ae82d148f01876f03a1f4afe weekly-11w50a f88e7c050cf88e7ec87f188d004c79fc f388f7e3ad02afb8373a425a36cad5f8455deb30 weekly-12w01a a1da27d48db6132a14444c2c7949c0f5 b5902c3f982bfeb017f6805d3125e38ea926b935 weekly-12w03a e3a4db9c2ef67dbdc7f20557c673fee1 c7964038cddcc127ae767efec22cc8cbae10c42a weekly-12w04a 4eb71d3cd4cdb29833eb25cca8b3dd54 6add7e893135777ff54028195a3f92ed6b2b9c31 weekly-12w05a (second attempt) cc510c6e88c3581962a6e8658aee9ae2 39449efaf44526132e5629e804ecf3cfffd8a8a5 weekly-12w05b 7544a148949c6cbb46114ba171762511 53a59f819089bf496406c9761674b50d0ee57356 weekly-12w06a 085dbcea5867dd1bc88ed3069fbb8758 7518ca0aa64156c1a55f4a8363e9578862adcd3a weekly-12w07a e2f462a7e6f437b7ae81316f495d7daf b6cdb5b4f34b25fd778313112190dd8758bf213b weekly-12w07b 4e075e09625612681d6ae28ee7d68beb dc5aa3d7f72a3b3aa0988b4c5d2377c18f81ef1a ClientMinecraft AlphaServer
Version Timestamp minecraft.jar md5sum minecraft.jar sha1sum beta-1.0_01 1292869768000 03bd20b870dbbd121de5dca98af4e1ce 4caf69885b64132e42d3ce49996dbdb1691d7111 beta-1.1_02 1293023696000 7d547e495a770c62054ef136add43034 e1c682219df45ebda589a557aadadd6ed093c86c beta-1.2 1294935268000 6426223efe23c3931a4ef89685be3349 ba05d7a97926c61c03cf956f7ae92f3bede9474e beta-1.2_01 1295011600000 486d83ec00554b45ffa21af2faa0116a f71a5b58c9bd0e458878d78a34c9fb35e97d5222 beta-1.3_01 1298470263000 4203826f35e1036f089919032c3d19d1 add3809d2c075e985d4b583632dac3d9c3872945 beta-1.4 1301589316000 71e64b61175b371ed148b385f2d14ebf f6dbca5223ea2a7e89806e93d0b18162b2d58c20 beta-1.4_01 1301991999000 9379e54b581ba4ef3acc3e326e87db91 6f157f26955c35006c1afa8b0479e0ce785fb864 beta-1.5 1303220253000 24289130902822d73f8722b52bc07cdb f5ce1699cd728213c21054fa2f1490d162b002b4 beta-1.5_01 1303302694000 d02fa9998e30693d8d989d5f88cf0040 e2a692e5e8160c84b29c834ecbf398618db9749c beta-1.6.4 1306418981000 5c4df6f120336f113180698613853dba b5d3bdb8a7b12d163651f4787ac6ca14689aab9e beta-1.6.5 1306595612000 2aba888864b32038c8d22ee5df71b7c8 90ed9854b43c4d031ed07381ea3ae3071a8bba6f beta-1.6.6 1306845669000 ce80072464433cd5b05d505aa8ff29d1 f95fe05711d09553ca2a9089f981741c13d6b8c4 beta-1.7 1309441055000 682419e9ed1a236c3067822d53cda1e4 ad7960853437bcab86bd72c4a1b95f6fe19f4258 beta-1.7_01 1309444501000 defc33265dfbb21afb37da7c400800e9 b0f67f3105e32b1a905d934f1e56117ef45d7148 beta-1.7.2 1309520900000 dd9215ab1141170d4871f42bff4ab302 7dc50cc5e2ff204a7283f0c7d38cd0370b49875b beta-1.7.3 1310111031000 eae3353fdaa7e10a59b4cb5b45bfa10d 43db9b498cb67058d2e12d394e6507722e71bb45 beta-1.8-pre n/a 7ce3238b148bb67a3b84cf59b7516f55 6789c69ede3aedf83b800c76bea56855d38a0afc beta-1.8-pre2 n/a bff1cf2e4586012ac8907b8e7945d4c3 44191f2895bf1e064269c9279778f2e3e9c3c9c7 beta-1.8 1315993659000 a59a9fd4c726a573b0a2bdd10d857f59 3139e9c29b2c74f59ea04de760ac2af5bc21b410 beta-1.8.1 1316075312000 f8c5a2ccd3bc996792bbe436d8cc08bc 6b562463ccc2c7ff12ff350a2b04a67b3adcd37b beta-1.9-pre n/a b4d9681a1118949d7753e19c35c61ec7 fdeef0129af130aa00702e53c37c5c4029b7d50e beta-1.9-pre2 n/a 962d79abeca031b44cf8dac8d4fcabe9 b0d40cf43b625631af65e2a645c34b533251da0e beta-1.9-pre3 (initial, bad) n/a 8c50b9d8d8d5a3a5bfa2e18d2fea7728 21d02c8bbf3bc35e7dc7909808147f8a01126811 beta-1.9-pre3 n/a 334827dbe9183af6d650b39321a99e21 5b7fe76a602b7511c97740e36dc25040ccb6e76b beta-1.9-pre4 n/a cae41f3746d3c4c440b2d63a403770e7 5c4831d9705f2e00e3cd993e89b822636492932a beta-1.9-pre5 n/a 6258c4f293b939117efe640eda76dca4 e109b297d2c4ee7a0bd6aed72f38f7e3185654cf beta-1.9-pre6 n/a 2468205154374afe5f9caaba2ffbf5f8 f0983e65cd1c0768b0d1fec471ce4f69173b8126
Version minecraft_server.jar md5sum minecraft_server.jar sha1sum beta-1.0 5b604526c8dae430c389d315e8e5eb08 5270b250d8a1c48f170d53b4b3874b01c55ec72c beta-1.1_02 93ca0782aa1b903b43f2e8c685c91b4d cc1bc7e0f46541053d5111e0dddd5c58286f2d5e beta-1.2 898dffced08b5f218493f9cd0333150a 2385685c0f1369eb2069858681ee6725ea4a4e7e beta-1.2_01 6a4802622360210b8f75a80bc4159792 4f2a8d6035dd8bde767b91613cd9ea03c65b465a beta-1.3 fd341dccafa8c1f5fb851505524151f5 5cc2aa79b477761cd229d1c3075a6a3afb2bc3ce beta-1.4 0696d954f292f85401a8dc9d6babcea9 b6e923a3438711a9a9c438ee6eb996a6f37950ef beta-1.4_01 cdcfd922abae8d6d6f25bdaba2774ae1 0b34fedf13b96829d256d722ebb966c55f893b45 beta-1.5 3e20218300c995effa5b1fdd3b9c74e2 5bef896515c1d6fbbdef9976b95c6a23534e4eb1 beta-1.5_02 edbcec2e58bd5a03954ba7d745dee604 a17bcc9bcbe0685dd485f9fb15764e85b5888619 beta-1.6.4 cbde8d4ef59494f488c472b33e711491 730f8d9484f8441816c89fa7093fc34bac98eb57 beta-1.6.5 565a3627a03a49e4a6e18d518a2e9d15 781e69c6881626f77c9f168ae4f307ae1422552e beta-1.6.6 0563ccb08d4dc84634d561b7f4bea596 e6c5db853f3b019599c24ce3d97b45bb7d8e02bd beta-1.7 5d685dd54fb4ba4a05fc20dea806e2c0 0d841f7f651822120650a2e700832626f8206d89 beta-1.7_01 b4b2e473ceb525026ba205642b8d9165 2838451ebb627d71e5d245952a61e9d71e284f6c beta-1.7.2 74376a139f932b9fcfc6caea6702a362 ee32a882e364c0021060853f5fcdf1b83e985904 beta-1.7.3 cc263aa969f2d8621c5443a5a18897e2 2f90dc1cb5ca7e9d71786801b307390a67fcf954 beta-1.8-pre 3733d045fb09ad9a5b94a89f6e1bea63 f77a3b3f48defde499d16d0aa7aaf65986c83f40 beta-1.8-pre2 d6e00c23a895978ba4544d59e64272a6 4cdbe68bef279d4624e78541965f09d42362f377 beta-1.8 d3dd75cccaa75b1df1401cc4e76a34d5 8cdfd85eaebfb1f0c70fd4b2d5301a547e2d4caa beta-1.8.1 0c0ed1f8198b37561971f838043838ab 79c4f3dc88d06db359dbf5cfedbbbd120d73bf4f beta-1.9-pre d4bcdbd0d4e75c96d0804b8a1f7ba527 c3597cdc781be976eb42204fff3af6631acb96c2 beta-1.9-pre2 f5d2a15f4b75d82b4ccc31ef66b650e7 71b61b8b3222e5eb9033545d9c743dd2d9732b63 beta-1.9-pre3 4f0149aa371435e36512c00220269b05 14e820fd32bea109ead9ef26345a5dfadd8ae3d4 beta-1.9-pre4 45b8a66e21d335bf626734c0ca3485f5 5452653944a5c8c05767dcc5f6ee0427ee736faf beta-1.9-pre5 69c68380cf198ce50b1f9ecaa8e4681d 7ec65beaaf1d3b619ca7effa91ff7d3d0fd168bd beta-1.9-pre6 963b90ab757793f10f584facdcd40a2b 3482a58d8ea938206f43db7a9d4b678b7876281a ClientServer
Version Timestamp minecraft.jar md5sum minecraft.jar sha1sum alpha-1.1.2_01 1285241960000 94346e1b8f6ad0e4a284314f0e29207b daa4b9f192d2c260837d3b98c39432324da28e86 alpha-1.2.2 1289417910000 6250fb17f8898c4d970d6bd03c229177 1c28c8431392641045b59e98a81877d7c94ff0ca alpha-1.2.6 1292492918000 ddd5e39467f28d1ea1a03b4d9e790867 a68c817afd6c05c253ba5462287c2c19bbb57935
Version minecraft_server.jar md5sum minecraft_server.jar sha1sum alpha-0.2.1 baca367c6da783de2b739ee939e096a6 c6217416ce92eb91d1511392f21f830746937418 alpha-0.2.2_01 0f62a8c36124f1fb432d234db7893d8f 729c2798c2781a6f8109d8dfe21cf0cc4ae2d16c alpha-0.2.3 311dcc896a3141383cd3c020a387812f 2bb3c32eb14f9fb6f98984de04cf9bdbc827d496 alpha-0.2.4 bedaa2a34904b96f6160035603e31773 bc5629edf607f166b8e86a5bfbde4dbaef31353d alpha-0.2.5 826af5f2ea2910e94b75b1a099b2b4bc f75f093fc2fb3ae649d41d1cab92bb86b199a3f6 alpha-0.2.5_01 20f0b11458e6f3df75e018a043dd73e0 5ce1d04d71a573ad0c87578a734879b4ea5d6682 alpha-0.2.5_02 a967b2de25519bb40f5ddc4244abfa39 6432a0da1ad8ebd0da593ee7a11bc34056d0a1af alpha-0.2.6_02 f196ae542ac9b14781a786d248e018bb 2939d4998fab5dcef33c27046ee34c53db151bc2 alpha-0.2.7 5684a1d3f70dfbbc0d0aafc9e108f262 f4d5a32b582b6f4d43a7d9c06297798be809f034 alpha-0.2.8 5858d9901aff321ce4305bd99489596f 4d1a4c2f1513b1c019b8ab1b720b8881caccd0d4 Additionally, it might be useful to have a rough mapping of Alpha client to server versions, since those didn't match up for most of Alpha. I didn't bother to go much further back than from around when I initially bought the game.
Alpha Client Version Alpha Server Version Notes 1.1.0 0.2.0 1.1.1 / 1.1.2 0.2.0 / 0.2.1 (update history is a little confused here, at least from what's on Notch's blog) 1.2.0 0.2.2 Halloween Update 1.2.1 0.2.3 1.2.2 0.2.4 1.2.3 0.2.5 1.2.4 0.2.6 1.2.5 0.2.7 1.2.6 0.2.8