Here's one that I know of: http://ramnode.com/vps.php

Other than that, I'm sure you can find something on webhostingtalk forums.

Check http://lowendbox.com/ , though YMMV.

http://serverbear.com/compare/vps is a great place to find these VPSs, they list some of the smaller services.

I rent one on BuyVM (http://buyvm.net/). I use it to run an IRC bouncer and an IRC bot.

cloudatcost has $1/mo small servers, or you can buy one 'permanently' for $35.