http://www.remote-exploit.org/index.php/BackTrack Backtrack
http://www.nubuntu.org/ Nubuntu
http://www.remote-exploit.org/index.php/Auditor_main Auditor
and there are probably more. But that shouldn't stop you if its what you want to do. Chances are these distros will have lots of tools you'll use, and a bunch you won't. Roll your own and put just what you want in it. You'll probably learn a lot in the process.
peace