Ryan H. (LDM) has been making copies of various album covers out of LEGO. His most recent one is a mosaic that incorporates 31 different LEGO colors. Here you can see his mosaic on the left, and the original album cover (Narrow Stairs by Death Cab For Cutie) on the right:
I'm not sure I could even give the names of 31 different LEGO colors, let alone use them all in a single mosaic. I have plans to write-up some techniques that different people have used to increase the palette of available colors for mosaics. Ryan here demonstrates one of the simplest: just make use of the wide variety of colors already available. There have been quite a few new colors introduced lately, which is great for potential creations (but not so great on the wallet!).