Why not: I can't find a distro that "stands out", rather than just fading in with the other choices out there. As much as I love some of the ones listed below or other popular choices, none really appeal to me over any of the others.
Why: It works doing almost anything you can think of, and it has a live CD.
Why: It is extremely fast. (Boots in 15 seconds, powers off in 5.)
Why: Extremely small and lightweight (10MB CD, 80MB HD), but doesn't use FLWM, so it isn't dreadful to look at.
Why: Only 25MB to start out with, plus is very easy to add new programs.
Parted Magic (Partition Utility)
Why: It contains tools that make it easy enough for a Linux newb like me to use. (Though I am getting pretty handy with cfdisk and slightly with fdisk.)