I would love to see (omitting courses already confirmed):
Indianapolis Motor Speedway
Watkins Glen
Magny-Cours
Aintree
Mid-Ohio (yeah, I know, but I live in Ohio)
Imola
Sebring
Monza
Spa-Francorchamps
Le Mans
Bathurst
Reims
A1-Ring
I would also like to see some ice races, like in sweden and michigan, also, hillclimbs, they are probably the oldest form of motorsport, and would be pretty cool.
In the totally absurd category (too long, or not enough still exists to accurately model the course):
Manx TT
Targa Florio (piccolo, media and grande)
Mille Miglia
Paris-Berlin
Yeah, I know that its a big list, but I love real courses. In all honesty, I can do without the made up courses, there are so many wonderful real ones out there.