http://reprap.org/bin/view/Main/WebHome
Ok it's not REALLY self-replicating.
UPDATE:
More here:
http://fabathome.org/wiki/index.php?title=Main_Page
And for those who can't be bothered building one, here's a halfway house:
http://www.emachineshop.com/
http://www.pad2pad.com/index.html
(An exceptionally cunning business model).
