Desktop
Motorola MC68EC020 CISC 14.18MHz (Aminga 1200)
Intel Pentium 133MHz (Socket 7)
AMD K6-2 300Mhz (Super Socket 7, clocked at 400Mhz)
AMD K6-3 400Mhz (Super Socket 7, wouldn't clock more than a few Mhz)
Intel Celeron 400MHz (Socket 370, clocked at 500Mhz - legendary chip!)
AMD Athlon K7 700MHz (Slot A, wouldn't clock at all really)
AMD Duron 750MHz (Socket A, clocked at 900Mhz)
AMD Duron 800MHz (Socket A, clocked at 950Mhz, still couldn't hit 1GHz, I crushed the core on the previous chip, this replaced it)
AMD Athlon XP 1800+ 1533MHz (Socket A, Palomino core, didn't clock it)
AMD Athlon XP 2400+ 2000MHz (Socket A, Thoroughbred core, clocked to 2,300MHz)
AMD Athlon 64 3400+ 2400MHz (socket 754, Clawhammer core, wouldn't clock much)
AMD Athlon 64 3500+ 2200Mhz (socket 939, Newcastle core, clocked to 2500Mhz)
AMD Athlon 64 3200+ 2000MHz (socket 939, Venice core, bought for a second computer, still runs in my Mum's machine now, would clock to 2400MHz at least)
Intel Core 2 Duo E6600 2400MHz (socket 775, Conroe core, clocked to 3000MHz and still running in my media machine/server)
AMD Phenom II X4 940 BE 3000MHz (socket AM2+, wouldn't clock much, 3100MHz or so)
AMD Phenom II x2 550 BE 3100MHz (socket AM3+, used/using in a test setup)
Intel Core I5 2666Mhz (socket 1156, Lynfield core, my main machine now, I haven't tried overclocking it yet)
Laptop
Intel Pentium M 1733MHz (Dothan core)
AMD Turion TL-56 1800MHz (Tyler core I think)
AMD Turion ZM-82 2200MHz (Lion core)
Intel Core 2 Duo T7500 2200MHz (Merom Core, socket P, my main laptop now)
Intel Celeron M 600MHz (whatever the Celeron used by the first Asus E701 was)
Intel Core 2 Duo P8600 2400MHz (Penryn)
Intel Atom N270 1600MHz
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I think that's all, but I do have a feeling I may have forgotten one or two I had.