I've just come across a great lightweight distro, the unfortunately named Plop Linux. The genius of this particular handcrafted distro is the number of ways you can bootstrap it. If there was ever a distro you might just be able to get onto your toaster, this is it! The developer has written his own bootloader which also allows you to boot other distros: I've used it to get Puppy Linux running on a machine that only has a Firewire CDROM and can't boot from USB.
Very useful, worth a look in Hot Picks I think.