I admit I voted for the TAM because I have one.
But excluding prototypes (clears, etc) I would have to say some of models I'd find the most collectible (in no order) are:
iMac 233 MHz, original (not super rare, but one of those milestone Macs a collector wants)
Macintosh Colo
ur Classic (I or II and the Performa 200 and 250)
Macintosh TV (because they're hard to find and crappy computers!)
Macintosh 128k
Macintosh ED (a 512k sold for educational markets, there was also a ED Plus)
20th Anniversary Macintosh (yes I plug my outdated page all the time)
Macintosh Centris 660AV (changed to the Quadra 660AV only a couple months later)
Power Macintosh 5420 (black case)
Power Macintosh 8200 (basically a 7200 sold outside North America in a tower case)
Macintosh PowerBook 550c (faster, black PB 540)
Macintosh PowerBook 100 (it's so cute! Plus it's another one I have.

)
G4 Cube
Apple Network Server (500 or 700) - My most wanted Mac!
Power Macintosh 7220 (crappy 4400 sold only in Aus.)
Not all the best computers in the world, but oh how I want them.