S939 X2 4200+ and several Pentium 4's ranging from 2.4GHz to 3.2GHz. They're not mine per se, but they're either close friends or family's computers that I do all the maintenance on. I can't convince anyone to upgrade from their Pentium 4's.
Oh! I built something for my girlfriend's son to play games on a while back. I purposely used old components because he was three at the time and the chances of it getting trashed were fairly high - AMD something-or-other at 1.2GHz, God knows what motherboard, 512MB of memory, Radeon 9800 XT, and a glowy case. It still plays all of his games to this day, and he's turning six in April. Except for spilling juice near (not on) the keyboard once, he's been absolutely excellent at taking care of it (so good in fact that they bought him a netbook this past Christmas), and he now types better than he writes...