Virtua Racing for twitchy arcade physics and high octane real arcade experience.
V-Rally: Extreme Edition by Eden Games. V-Rally just has a more in depth and hardcore feel to it than Dirt games without being geeky or boring. It has excellent textures and is extremely challenging but for some reason unbelievably fun. Also it has a track editor which is excellent.
Dirt 2 because I probably played that the most historically and well, it's Codemasters.