There are a few cars I'd like to see in the game.
Most Interesting:
2005 Chevy
C6 Corvette
1991 Chevy
S10 Syclone
2006 Dodge
Magnum Police edition
2004 Dodge
SRT-10
2004 Dodge
SRT-4 Neon Extreme Lightweight
~2004 Mazda
RX-8 turbo concept. Very cool concept from Mazda Australia.
Silly, but interesting:
2004 Rolls Royce
Phantom (6.75 litre V12)
2005 Bently
Arnage (6.5L V8)
And of course the various GM
concept cars from days gone by.
Historical cars that are interesting:
MGB
Triumph
TR6
1966 Lamborghini Miura fastest car in 1966, 352hp V12, 170mph
1987 Ferrari F40
1992 Yamaha
OX99-11 I remember reading about this and the McLaren F1 at the same time as they were both rather similar.
Super cars:
2004 Bugatti
Veyron 1000hp sounds fun.
2004 Koenigsegg
CCR Possibly the fastest production car in the world.
1997 McLaren
F1 Getting old, but can't be beat.
1996 Vector
M12 (or WX3 or W8) Vector deserves to be in there!
2002 Mosler
MT900 Perhaps not the highest top speed in the world, but likely the quickest around a track!
2004 prototype Chrysler
ME Four-Twelve This is going to be one quick car!
200x Ferrari Enzo, etc
Lamborghini Diablo GTR, etc
I know the reasons for there are licensing issues to contend with for at least three of those brands, but some of those cars could make it into the game. I'd rather see some of those different vehicles than 15 very similar Subaru WRX STi cars. It's a great car, but I'd rather see some others in the game before getting 14 additional variations on it.