MineCrak has a second opening post directly below. It will likely be kept much-more-frequently updated, with all the newest-and-best versions, tips, etc.
4096BlockIDs: (Requires ModLoader and Forge)
NOTE: After MC 1.2.5, I am no longer planning to maintain this mod. I have released the source code (see Developer Notes below), and I hereby give permission (and, in fact, thanks) for anyone to do whatever they like with the 4096IDs source code, so long as they give my code credit.
Have you installed a lot of mods? Ever been annoyed by how few IDs 256 really is? Especially with the addition of Forge, which allows you infinite sprites?
No more! Now, with 4096BlockIDs Mod, you have 4096 (duh!) available Block IDs. That means you can have 4096 different Blocks! How could anyone ever run out?
Also, for those of you who haven't looked into Minecraft 1.2.3's code, Anvil format supports saving up to 4096 block IDs, but Minecraft 1.2.3 is still incapable of actually using those extra IDs. I rest assured that this will be fixed in Minecraft 1.3.*, but until then, I'll keep updating this mod.
Current Mod compatibility.
4096IDs Standalone Client for MC1.0.0 (Forge 1.2.4) - this may also require ModLoaderMP.
-Alternative MediaFire Link
4096IDs Standalone Client for MC1.0.0 (Forge 1.2.0) - this may also require ModLoaderMP.
Client 4096IDs for V1.5.3 test versions 4 and 5 (Beta1.8.1) - Beta 1.8.1 Cubic Chunks compatible Patch for Cubic Chunks V1.5.3 T4 & T5. (Not Vanilla compatible!)
4096IDs Standalone Client for MC1.2.3 (no Forge).
Warning: for some reason, there have been various bugs (that I've been having a hard time finding the causes of) in 4096IDs Standalone for MC1.2.3 Forge1.4. I advise you to back up your saves. (NOTE: If you are a modder, and want to try your hand at figuring out what's wrong, feel free to look into the source code in the developer notes spoiler).
4096 IDs Standalone Client for MC1.2.3 (Forge 1.4) direct link.
4096 IDs Standalone Client for MC1.2.3 (Forge 1.4) AdF.ly link.
(Not sure what was the problem in the MC1.2.3 version, but I've tested, and it is fixed in the 1.2.5 version.)
4096 IDs Standalone Client for MC1.2.5 (No Forge) direct link.
4096 IDs Standalone Client for MC1.2.5 (No Forge) AdF.ly link.
4096 IDs Standalone Client for MC1.2.5 (Forge 126.96.36.199) direct link.
This is apparently a patch for 4096 IDs Standalone Client for MC1.2.5 (Forge 188.8.131.52) that should update it for more recent versions of Forge. If it doesn't work, tell me, but don't blame me.
As of Minecraft 1.2.3, Cubic Chunks will offer built-in support for 4096 IDs. So, first, you only have one mod update to wait for if you want them both; and second, don't expect a 4096IDs CubicChunks patch here.