The sysadmins over at Tummy.com are selling a lot of their old gear. I'll be picking up a few servers, one to use as a new network firewall, and one to serve as my new svn server. Their prices are pretty reasonable for such old hardware, but if you're planning on running Linux, they're pretty cheap boxes. They even have equipment for sale to build your own Asterisk server.
All the stuff for sale can be found at http://forsale.tummy.com/. They also update pretty regularly right now, so keep checking back!