Among the different types of racing games you can find, I specially enjoy the micro machine ones. You know, the kind of racing game with aerial perspective and small-sized, cartoonish cars.
Mad Race is an excellent example of these micro machine driving games. It challenges you not only to arrive to the finishing line in the first position, but also to get rid of your opponents. To prevent you from getting bored of driving, it provides you with a ton of weapons and other bonuses you can use against other drivers.
The game supports multiple player profiles and two main gaming modes: single race and tournament. You'll have access to different tracks and cars, though not all of them will be available from the beginning and you'll have to unlock them as you progress through the game.
Mad Race features surprisingly good graphics for a free racing game, and will surely provide you with hours of fun. I have only one complaint and that refers to the game's camera, which I found a bit dizzying at times.
If you're looking for a simple yet fun driving game, Mad Race is definitely a great choice.