Intel 286, 16mhz (no idea about o/c)
AMD AM-386 SX 40mhz (O/c to 50mhz cause post beeping)
Various Intel 486's, all complete POSses
AMD K6-200 (Didn't like o/cing)
AMD K6-2 450 (o/c to 495Mhz)
Intel Pentium 3 666 (o/c, bah, these things probably would but the boards don't let you)
Intel Celeron 1Ghz (o/c to 1.45Ghz ^_^)
Intel Pentium 4-B 2.4Ghz (o/c? Hah, it's a POS, especially in my system)
Those are the ones I've personally owned in my own systems, but I've had other systems slip through my hands and in my house, etc..