Slackware will easily fit in 3GB. Debian too. Depends what you install of course.
I've installed Slackware on a 128MB compact flash card (it was pretty cramped though).
If you want to be hard-core, how about Linux From Scratch. You can configure that to fit into pretty much whatever you want.
Last edited by ioerror; 11-22-2005 at 02:56 PM.