Project CARS is what I'm currently waiting on. I hear Assetto Corsa is good, but it has too few cars for my taste at the moment. I might try it if they expand the selection substantially. iRacing is the defacto sim to my knowledge, but it's subscription based.
On the off chance that you still enjoy more arcade like titles, or even a kart racer, Sonic & All-stars Racing Transformed is one of the best cart racers in over a decade. I'd easily compare it to Diddy Kong Racing, Crash Team Racing or even Mario Kart 8.
Also, to those who have played it, how is Grid Autosport? I wasn't overly fond of the first two.