Mine has to be Nurburgring Nordschleife. Awesome ass course, I've seen videos of people running it irl (specifically this chick goin all out in an M5). I've pretty much mastered the course with a 190E (which I actually plan on buying a 2.6 5-speed irl soon). Course has a good mix of all out speed, high speed cornering and tight twisties. You can't get better than that 
Yours?
Yours?