Does anyone have any recommendations on renting a nice car in Frankfurt? I've rented a "luxury" class car through National in the past and gotten a Mercedes C180, which was quite nice, especially at $90/day (I'd much rather have a C180 than the Cadil-olsmo-buick that $90/day gets you in the states).

However, if I was interested in something a little more unique, like say an Audi TT or an M3 or maybe even a 996, does anyone have any recommendations for companies to use? Preferably with pickup/dropoff at the airport.

One last question: since Nürburgring is technically part of the highway system, does that mean I could take a rental car out for a spin around the 'ring?