Wow, I've had more CPUs than I thought 
Intel 286 (8Mhz, 12Mhz in 'turbo mode'
)
Intel 386 (16Mhz)
Intel 486DX (25Mhz)
Intel 486 with 586 overdrive (100Mhz)
AMD K6-II (450Mhz) - this was an amazing upgrade at the time!
AMD Athlon XP2100 Palomino (1733Mhz) - fast, but very warm.
AMD Athlon XP2500 Barton (1833Mhz) - first self-built PC. The chip which got me into overclocking, got it to 2400 on my trusty NF7-S if I remember rightly!
AMD Athlon XP2400/2500 Mobile (1800/1833Mhz) - had several of these. Ran the last couple at 2500-ish.
AMD Athlon 64 3200+ Winchester, socket 939 (2000Mhz)
AMD Opteron 146 (2000Mhz) - clocked it to 2900, nice chip.
Intel Core 2 Duo E6300 (1866Mhz) - cracking little CPU, 66% overclock in minutes.
Intel Core 2 Quad Q6600 (2400Mhz) - currently running at 3150. Still amazed at how much power this CPU has - getting on a bit now, but can't see me needing to upgrade for at least another year.

Intel 286 (8Mhz, 12Mhz in 'turbo mode'

Intel 386 (16Mhz)
Intel 486DX (25Mhz)
Intel 486 with 586 overdrive (100Mhz)
AMD K6-II (450Mhz) - this was an amazing upgrade at the time!
AMD Athlon XP2100 Palomino (1733Mhz) - fast, but very warm.
AMD Athlon XP2500 Barton (1833Mhz) - first self-built PC. The chip which got me into overclocking, got it to 2400 on my trusty NF7-S if I remember rightly!
AMD Athlon XP2400/2500 Mobile (1800/1833Mhz) - had several of these. Ran the last couple at 2500-ish.
AMD Athlon 64 3200+ Winchester, socket 939 (2000Mhz)
AMD Opteron 146 (2000Mhz) - clocked it to 2900, nice chip.
Intel Core 2 Duo E6300 (1866Mhz) - cracking little CPU, 66% overclock in minutes.
Intel Core 2 Quad Q6600 (2400Mhz) - currently running at 3150. Still amazed at how much power this CPU has - getting on a bit now, but can't see me needing to upgrade for at least another year.