Trackmania is awesome, there is also a free version called Trackmania Nations, it's most fun online though. ^^
I havn't played DiRT yet but it is meant to be very good, the minimum specs are very high though (apparently you need an 8800gts or better for it to run on max settings smoothly), so don't expect it to run too well on your laptop lol.
I just had a quick look on IGN and there doesn't seem to be much else in the racing genre for the PC that is much good aside from older Colin Mcrae and NASCAR games, though Flatout 2 got 8.3 so it may be worth a look.