Hmn, this is tough...
1) Bugatti Veyron
2) Ferrari 599GTB
3) Porsche 997 GT3
4) Ferrari F430 Scuderia (track version)
5) Golf GTI Mk5
Didn't make the list: Audi RS4, BMW M5 (any version), Ferrari 612 Sessanta (60th Anniversary), Lamborghini Murcielago LP640 (in battleship grey, natch), Mitsubishi Evo X (I'm quite taken with this), Mitsubishi Evo V, Nissan Skyline GT-R R34, Porsche 993 Turbo, Porsche 356, Volkswagen Microbus (with 911 engine
), VW Beetle, VW GTI Mk1... err... I think that's all I can think of for now.
Didn't make the list list edited to add a couple
Quite old school, none of this Koeniggssesegegegeegeg or Zondas for me.