I just recently rediscovered the Trans Am series and found the racing to be pretty spectacular. The series is split into 3 classes: TA, TA2 and TA3. My personal favorite and favorite among most is the TA2 class as its the biggest and most consistent class, TA is just a faster, more insane version of that, and TA3 is productions cars.
Here's their opening race at Sebring in which all 3 classes take part:
My Personal Favorites of the season are the Lime Rock Park and Mid Ohio races when TA2 is in their standalone races.