The vette '69 and the cobra sound like the only true V8's in the game - that is, awesome. The tuscan (without any mufflers) is downright great. Whilst most cars share exhaust sounds, i reckon this one is pretty rare.....
Fiat Coupe and Punto GT are awesome - sound like Chrysler Hemi's without any mufflers.
Also the Impreza STi Version V 1998 makes a cool sound, it's the only realistic-sounding model of Impreza in the game.
THe Honda's and Mitsubishi's mirage sound is also a nice twin-cam wail.
The Punto GT is in Fiat's new car line-up. I meant that if you dnt put on any mufflers it makes a wicked sound
It costs around 16,ooo Cr and is 130hp turbo, 1000kg It's brill! and it whups the asses at the 80's car cup at Trial Mountain (Mine is Broom yellow with 191hp)
The best of course is the fully tuned Corvette ZR-1. Its the best when at high rpm's. I say the second best is a stock '99 SVT Cobra. It has the kick-ass super charger whine.
id have to say, my plymouth GTX, with full surround sound on , sub turned up, rattling the pictures off the wall, then you crack the throttle and go deaf