Old but Gold. The Magnetic Fields Rally Championship from 1999 has just been re-released on budget and updated for XP. Before you scoff at a 8 year old game, this was a definitive title in the genre. Today's hardware can run it at maxed out detail. Some of the courses are over 20 miles long and all based on real locations from the GB Rally. Also, unlike some other rally games, you don't need to come in the top five etc. to move on to the next course. The emphasis is on keeping your car in good enough shape to make it through all of the six stages of each individual rally (and there are six of them).
Failing that, then RBR obviously or wait for Colin McRae Dirt which is due out next month.