Great thread! Hello to some of my Muscle Car friends (without Mario I'd still be trying to get GTL to work at all!), as well as that other gang of 'cyber-dudes' who've made GTL so much better - the NoGrip modding wizards!
Ahvenisto, Cadwell, Trois-Rivieres, Monaco, and lately Halle-Saale, Rockingham, and Miseluk have been my favorite twisties to throw the '69 Camaro around with a crowd of AI.
But for 'hill climb' or 'rally' type solo blasts, Red Rock and Joux Plane are tough to beat.
I have Eltsu for rFactor, but not GTL. Eltsu's an absolute gas to fly around on, and I bet it'd only get better with GTL!