Heh, my somewhat flighty approach to PC use means "main rig" is a bit of a grey area for me - whilst I've occasionally had only one PC, or one PC that I've used significantly more than another, I've usually had several PCs running that have rotated in primacy.
But, fwiw, this is probably as close as I can get. Where a rig had CPU upgrades I've denoted the CPU progression with ->. Where I mostly used a laptop I've only listed the laptop CPU; for times where I had both a desktop and a laptop that I used equally I've included the laptop in brackets after the desktop CPUs.
286 12Mhz
Duron 1200 -> Duron 1600
Athlon XP 2600+ Thoroughbred B
Turion TL-52
Q6600 -> Pentium E5300 -> Q6600
Phenom II X4 905e (Pentium SU4100)
AMD A10-4600m
But that's probably not even half the PC setups I've had over the years...