TinyCore if you want minimal and hard work (http://distro.ibiblio.org/tinycorelinux/welcome.html) {Damn Small Linux is dead. TinyCore is sort of the result.}

Puppy if you want, well, I dunno, but it has a loyal userbase (http://puppylinux.org/main/Overview%20and%20Getting%20Starte...)

or there are a gajillion "minimal" versions of Ubuntu. CrunchBang is one, but there are many more.