[I don't remember if this was already posted somewhere on the boards, but even if it is, it's worth repeating]
McKeel Hagerty runs an insurance business tailored to limited driven or dedicated showcars or collector cars. A well known entity in the showcar/collector community. Every year he selects from the current crop of vehicles and identifies the ones he sees as future collector cars. Here's the list for 2008:
Cadillac XLR-V Roadster
Lotus Exige S
Audi S5
Mustang Shelby GT 500 KR
Chevrolet Corvette Z06
Smart
Subaru Impreza WRX STi
Honda S2000 CR
Pontiac Solstice/
Saturn Sky <--------
Dodge Charger Super Bee
CarDomain Car Blog: Top 10 Future Collector Cars?