Amazingly, in 1.1, I've found a game-breaking glitch that many player have probably looked for before! A Duplication glitch!
First, make a cobblestone (or any other block as far as I know) frame 4 wide. Then from each end, extend it several blocks. Then add water at the very back of the structure. If the water flows out of the frame, then extend the blocks. If there are blocks leftover, then get rid of them! Next, make a Nether portal in the ground at the end of the blocks and then ignite it! Finally, place a crafting table 3 blocks away from the portal frame on the blocks.
Now that you have set up your duplication "machine", here are the steps to duplicate any of your items:

1.Get the item you want to duplicate.
2.Get into the water, click the crafting table and put your item in it while you go through the Nether Portal.
3.Woohoo! Dup'ed item!

Tip you NEED TO KNOW:
1.What you have essentially done is create an item that produces infinite of it's kind, but cannot stack with any other block (even if it looks like the same block).
2.To obtain "normal" items of that kind, just place the "infinite" item in a chest and right click! Remember, do NOT stack the "infinite" item with the "normal" item.

If you have questions, leave them in the comments below! Rate this up so people know!

Also: This does NOT work in SMP for those of you wondering. This only works in Single Player!