My first computer that wasn't a calculator or game console: the Apple //c powered by, I believe, the WDC 65C02 at 1.023 MHz. At university, I bought my first proper notebook, the PowerBook 145 (Motorola 68030, 25 MHz). This was eventually stolen by a flatmate and replaced by a PowerBook 165, if I recall correctly (same cpu at 33 MHz)...
From the late '90s onwards I used mostly x86 cpus, owing to poverty:
Pentium, 166 MHz
iMac G3 (PowerPC 750), 400 MHz
Celeron 366 (Mendocino), overclocked to 550 MHz
Celeron 300, overclocked to 450 MHz
Athlon (Thunderbird), 800 MHz
Pentium 4 (Northwood), 2 GHz
K6 III, 400 MHz
Athlon XP 2500+ (Barton), 1.83 GHz -- running two of these
Pentium III (Coppermine), 866 MHz -- also two
Now building: Intel P35 system round a Xeon E3110 (Wolfdale), 3 GHz... Also have an Athlon 64 3200+ and X2 3800+ sitting unused at the moment. When I win the lotto, I will return to Apple and buy a Penryn-cpu MacBook Pro... Am currently typing on my girlfriend's MacBook (Merom, 2 GHz).
Edited: dang, remembering more all the time...