Good Old Games have a 50% off sale on racing games. Due to licencing restrictions Good Old Games will no longer be able to sell Colin McRae Rally 2005 from the end of this month. The game is nearly 4 years old, but it's still an excellent rally game. not quite as good as his last Rally title Dirt which was released several months before his untimely death. There are a few other titles but this is easily the best one.
http://www.gog.com/en/gamecard/colin_mcrae_rally_2005
Flatout a stock car racing game is also a great title, but I'm not sure whether that is included in the 50% off deal. Because I've already bought it, I can't see the price (it won't let me)
http://www.gog.com/en/gamecard/flatout
You can get Flatout 2 from fileplanet for a reasonable price. It's a big improvement on the first one. both the flatout games have a massive list of breakable objets in game (numbering in the thousands). The final one in the series called Flatout Ultimate Carnage is the best one, though it's basically a remake of flato 2, with all the same tracks but with an overall of the graphics and the addition of more cas to race against. All three games include a demolition Derby mode as well as some mini games that are very entertaining, for example theres one called high jump where you have to race your car at speed towards a giant high jump, when you get to a certain point you have to slam your breaks on which causes the driver to smash through the windscreen and fly high into the air. The rag doll physisc which is a small feature of the game comes into play in the mini games. There are upwards of 18 mini games in the 2nd and 3rd titles and include some wacky themes. (Darts skittles,, soccer, long jump plus loads more, all of which involve you causing your driver to leave the vehicle forcibly)