What cars from the last 20 years will be collectibles?

[Goodspeed]

Probably a lot of recent/current domestic muscle. These are some I can think of off the top of my head

Mustangs:
Shelby GT/GT-H Mustangs
'00 Cobra R
'03-'04 Termi
Saleen Parnelli Jones SpEd
'08 Bullitt
Roush P51R
Factory Drag Pak Mustangs
Saleen S281/S351 Mustangs

Camaro SS/Firebird Trans Ams
-35th Anniversary
-Firehawk/SLP-prepared 4th gens
-GMMG Camaro
-Berger Camaro
-Upcoming Camaro variants

And the usual Corvettes, 50th Anniversary, Z06's, ZR1's, perhaps Callaway/Lingenfelter variants.

Vipers - GTS-R, ACR, SRT10 ACR. Current SRT8 Challengers too.

The Ford GT/GTX-1 I see becoming highly collectible, perhaps the Mercury Marauder to some extent.

Its hard to judge Japanese cars in terms of collectivity. I doubt we'll ever see them on the scale of Barrett Jackson and other big name auction houses going for hundreds of thousands or more. I think they'll remain a niche collectible wherein certain people will pay top dollar for them, but they won't be regarded as collectible on the whole, at least here in America.