writes "ExtremeTech published a review of 4 Linux live distributions that do not require installation and run off a CD. Knoppix, Feather Linux, Gnoppix and MEPIS Linux were researched, with Knoppix winning the competition (and Gnoppix not graded, since it's still in beta)."
One more (of the seemingly infinite number of live distros) I've recently tried and been happy with is called Slax, and is what it sounds like -- a live Slackware distribution. Slax worked great with my finicky older Toshiba laptop. (However, slax.org appears to be down.)