The Live CD List is a directory of live CDs with extra features including voting, file sizes, download links, Wikipedia links, and Distrowatch links. The list is mostly Linux CDs, but there are also Windows, DOS, Solaris, and BSD live CDs on many different processor types. Search functionality allows you to find a live CD meeting your needs.
I use two live CDs right now. My Ubuntu desktop CD for showing off Ubuntu, and my GParted CD for partitioning new systems.