Cars I tend to use on the 'rnig:
AE86 on N2s: Not the fastest car available, but has the right pace if you want to take your time, and it won't bore you to death either. Very controllable car, and will fly into most corners without a hitch, and with some oversteeer possible with some feint motion, it can slide through a few corners well. A good car for learning the circuit and how to get the best from it. Not only do I like to use the standard car, but I've got a heavily tuned model with a turbocharger, which is fine around the ring, though I might try out the supercharger and see if it's differnet power characteristics are any good.
Mazda MX-5 (any): SImilar to the AE86, but even more agile. The balance makes these things very easy to control in just about any situation.
RUF BTR on any normal tyres: A modified version of Germany's most famous hypercar, combined with Germainy's ultimate circuit. Not just that, but a powerful rear-engined car coipled with plenty of elevation changes and tight, challenging bends makes every lap feel like a significant life event.
BMW M5 on normal tyres: A superbly fast sports saloon, it corners unike any other car of it's type, and the 7-speed gearbox mkaes light work of acceleration away from corners quickly. The engine note even seems to resemble an F1 car.
Mitsubishi Lancer Evolution VIII GSR on N2s: The four-wheel drive system works pretty well here, as does the six-speed transmission. This car's superb brakes allow you to get away with hitting the anchors rather late.
Honda NSX Type R ('02) on N2s: Very light and agile feeling car, Feels a bit twitchy on faster corners as with many high speed MR cars, but can take tighter corners very well and is reasonalby controllable.
BMW M3 GTR Race car: Being German, it obviosly feels at home on the 'ring. It's also a pretty controllable car with the sort of pace you'd expect from such a car.
AMG Mercedes 190E Cosworth: Fast, controllable, and has some retro value to it. Handles just about every situation brilliantly.