So here goes  
 
486DX33 --> 486 DX4-100 --> Pentium Overdrive --> Pentium 166 --> Pentium 200 --> PII 333 ---> PIII 750 --> PIII 1Ghz ---> P4 2.66 --> P4 3.0 HT --> X2 4800+ --> Q6600 --> Q6700 (current)  
 
with each platform change came the associated Motherboard and RAM change  
 
Thats going back from the early 1990s to present day  

8086 --> AMD K2 @166MHz --> Intel Celeron @700MHz --> Intel Pentium D @3.4GHz (OC'd 3.8GHz)

486(not sure of the specific model as I was young)--> Pentium 75--> Pentium II 333-->AMD K6-2(worked on a lot of them and some of the early K7's in college)--> Pentium 4 2.4GHz--> Pentium 4 3.2GHz--> Pentium 4 EE 3.4GHz--> C2 Q6600

Texas Insturments (forget model, but you had to hook it up to TV and program it with old school BASIC)>486 SX 25>Packard Bell P133>Gateway PII 400>Athlon Slot A 700>T-Bird 1.6>A64 3800+ 2.2>Opteron 185 2.6>Intel E6750@3.6.

P200 with MMX (F-yeah, MMX baby - that really made all the difference), P3 900, P4c 2.4 @ 2.8Ghz, Core 2 Duo E6400 @ 3.04Ghz.  
 
Prior to that I had used 386's and 486 at school but at home I had an Amgia 1200 (I upgraded this so I had two floppy disk drives, very handy for playing Monkey Island 2 and it's 12 discs!) and before that an Atari 500 ST.

286 -->  Pentium 100 --> Pentium 3 500 --> Pentium IV 1800 --> Athlon XP 2800+ (Barton) -->  Athlon 64 3200+ (single core) -->  Opteron 175 (dual core)

286-8 MHz, AMD 386 DX 40, 486 dx2 66, AMD K5 P133 (100 MHz), Pentium 133, P200 MMX, Cyrix 233MX, K6-2 400, Athlon Slot A T-bird 900, Athlon 1300@200 OC'd to 1400@266, Dual Athlon MP 2000+, X2 4000+, Intel Q6600@ 3.2.

286 -> 386-> 486->-486>Pentium 200Mhz -> k6 2 300Mhz -> P3 800 (notebook)-> P4 2.4 -> Pentium M (notebook)  -> P4 3.4 - > core 2 duo E6400 -> core 2 duo 5250 (notebook)  
 
 

Systems that I actually owned myself: PII 450MHz, Athlon 1GHz, Athlon XP 2800+, Xeon E3110
 
Before that it was my parent's and the early ones I don't event remember the name: 286, 386, 486DX2, some early AMD crap 133 MHz (damn they sucked back then ...)

---------------
The capacity to learn is a gift; The ability to learn is a skill; The willingness to learn is a choice.  - Rebec of Ginaz

Pentium 166 --> PII 333 ---> PIII 1Ghz ---> Athlon 2000 --> Athlon 2100 --> X2 4400+ 939socket(current)  

8080A --> 80186 --> 68030, 80286 --> Pentium --> Pentium II --> Pentium III --> Pentium m --> Pentium D 830 --> Pentium D 940
 
D955XBK constrains the CPU choices, unfortunately.  Next will probably be an E6750.

z80, z80a 68000, 68020, 286, 386, 486sx, 486dx, p75, p90, p120, C133+, P200, p200mmx, P2-233, Celeron 300a, P3-500 Copermine, 2xP3-733, duron 800, Athlon 1400+, Athlon 2200+, athlon 3200+ Sempron 2800+ P4 2.6 HT (462) Athlon 64 3000+, 3500+, 3800x2, q6600

Cyrix smoething-or-other -> PIII 700 -> PIII 1.0 (same board) -> E2140 (only 5 months ago!) -> E2160 OC'd to 3.0 (2 days ago)

Pentium II (not sure the speed), Athlon XP (not sure the speed), 2 Pentium 4's 2.8 and 3.2, and a Core2 T7200

Texas Instruments TV PC
TRS-80
Tandy 1000
P90 (edit: my 1st brand named - Packard Bell - after this point I started buidling)
Cyrix P100+ / 150+
AMD K2
AMD K3 and K3+
P233 MX
PII 400
PIII 800
AMD Thunderbird 1ghz
AMD XPAthlon 2100+
P4 2.66ghz (533FSB)
P4 3.0 HT (800FSB)
C2D 4300+ (stock 1.8ghz) @ 2.7ghz
C2D 4400+ (stock 2ghz) @ 3.0ghz

Future outlook... Q6600 upgrade perhaps later in April.... maybe.

Commodore C64/Vic20
486sx 15mhz(was an old tandy sensation)
Pentium 75Mhz
Pentium MMX 166Mhz
Pentium 2 300Mhz(SL2YK Retail Deschutes OCed to 450Mhz)
Athlon 1.2ghz Slot A T-bird
AthlonXP 2100+ Socket A Palomino (K7-2 in reality)
Athlon 64 X2 4200 65w Windsor
Currently running AMD Phenom 9600BE at the specs in my sig.
 
Granted I also still have an old Dell Latitude CPi A with a mobile p2 366mhz working to putter around with old Win98 stuff and a wireless card.

 
 
 
Was your Z80's in a Aquasius ?
 
 
 
Mine were:
 
K6 200mhz, K62 400mhz, PIII 866mhz, 1800+, upgraded to 2400+ (future....waiting for Nahelem)

486 (no idea what model, i was like 9 years old)> Pentium 133>Celeron 400MHz> AMD Athlon 1GHz> Intel E6300 (1.86 stock, oc to 2,1)

I may be missing a couple:
 
6510 (Commodore 64)
486SX-25
AMD 486DX4-120
P166
P2-333
P3 (forgot the speed)
AMD Athlon 1200
Athlon 1900+
Athlon 3000+
E6400
E8400

I want my next cpu to be a  Advanced Micro Intel Device (aka AMID) photon3000 Photon processor!