stunts.
http://www.youtube.com/watch?v=-CITIXlw_T4
It's a lot of fun to make your own tracks, especially seeing how the track pieces can be a bit crazy lol.
Oh man, that game was awesome.
Sadly I dont know any games with customizable tracks. Except for one, but I cant remember its name.
I was about to suggest this game. You gotta love that speed-lock/flying car bug.
Setup 1 loop and a long enough pipeline ahead, drive any car (INDY preferred), on manual, set to top gear, go through loop once and make sure to be on constant looping, reach 255 mph/kph, aim for the pipeline if you can find the right way out and not fly back at the start/finish upside-down in the sky, drive on the ceiling of the pipeline; but be closer to a wall so you bit the end of the barrel on the way out, spot your house from the new height.
Another neat bug is to make a complete circuit (tiny), and build an impossible course. Unfortunately, these only work best as time trials, and you can't race against the computer in them, but you can have one hell of an adventure, since error-checking is only from the start/finish onward until a complete circuit is made sans errors. it can care less about what's outside it's course; meaning, you can make your own city/landscapes in the distance, complete with buildings and streets, or make courses that'll make the error-checker cry.
I think I recall someone making a retro-remake of this game with better graphics. But so far, it looks like the graphics and the classic elements are all it has going for it so far. I haven't checked up on it recently, so i don't know if it got better. I'll provide a link when I find it.
EDIT:
Seems to still be in production/still alive. Then again, maybe not, according to the timestamp of the latest news entry.
Link:
http://www.ultimatestunts.nl/