I LOATH american muscle cars...I am not into japanese tuners either. As far as I am concerned in the game all the skylines, type-rs, corvettes, camaros, mustangs, evos, etc blow (they really blow actually).
I love my Subarus though! Give me any RUF over just about anything. The Zondas just rock. The TVRs are sick. Tommy Kiara is amazing...I do like my japanese race cars though. I like my WRC cars too. I like my Cobra (yes I know it is sorta kinda american) and I love my 187hp Mini...
Part of what rocks about GT3 is it offers alot for everyone no matter what your taste is. It IS scewed a bit to japanese cars but given the game IS from japan that is to be expected.
I personally would like to see some of the following...
-Classic 1950s Euro sportscars (jags, Alfas, Maserattis, ferraris, etc)
- Porshce 911's thru the years (40 years this year)
-More british cars (Vauxhall, Seat)
-More Italian cars (anything red)
-More German Touring cars (race car Audis...we have ALL the japanese supercars, why not)
-LeMans cars (vintage and current)
Oh and given I am a HUGE F1 fan give me post 2000 F1 cars...
FIA sportcar prototypes would be nice, both SR1 and SR2 classes