I don't have anything unique to add to the list, and it seems like there are definitely a few models that are in demand by many- myself being no exception
My desired, in order:
PowerBook 1.5Ghz G4 12"
any B&W PowerMac G3
G4 Cube
PowerMac G5
And just for the heck of it, 'cause work is super slow today, here's what I've owned:
Performa 6200... I believe it was a 160Mhz 603? I was very young at the time.
Performa 6400, 180Mhz 604e
PowerMac G3 266Mhz (I loved that thing... flashed a PC Voodoo3 2000 for Unreal Tournament. Sweet.)
iMac DV G3 400Mhz (GPU blew... again, young and foolish)
PowerMac G4 DP 867Mhz MDD (Just got rid of that one, gave it to my sister... nice machine)
and my latest, a late 2007 Alu iMac 2.66 Core Duo with a ATI 2600 that I'm happily overclocking.
I also owned a few Apple IIe, which I bought for $1 each from a school. I honestly don't know where the heck those went... probably in my parents barn.