I have been looking at several for a slightly less powerful machine. I have tried some and not tried others but:
tomsrtbt - floppy-based system, console if I remember corretly
Sisela - another floppy-based one, again I think it was console, not sure
Small Linux - wrote it down, don't remember anything about it
Tiny Linux...pretty much pick any word that means small, append Linux, and you'll probably find a distro
Also there is something called LinuxTiny that I started reading about and planned on looking into after trying out some earlier things on my list
Core linux is a cut down version that I was planning on trying, but never got around to.
Then there are the small CD/USB distros: Puppy linux, DSL, etc
Also you may want to look into some of the older Slackware installs. I had the best luck with Slack-based distros (though my not-really-VGA-standard screen managed to defeat even these)
There are a bunch on Freshmeat. I know there is at least one that seemed to be a fairly small footprint that I wanted to try but can't remember the name for it (I'm at work). I think it was based around Slack 7-ish and was the basis of workshops in several cities...sorry, can't recall off the top of my head.