What is the best racing game for xbox 360 or PC?

I'm considering buying a 360 and was wondering if there were any good racing games out for it. The greatest racing games I've played are Gran Turismo 3 and 4. When I first got a PS2 back in 2002 and first played A-spec I was smitten with it: the graphics, the customization, the variaty of cars from dirt track rally cars to formula 1 race cars, I loved every bit of the game and spent many sleepless nights advancing in my virtual racing career. I also liked playing Juiced for the PC a lot (nothing compared to GT3 of course). I liked the customization options and the betting aspec of the game but it constantly crashed on my PC, usually during a pink slip race which caused me to lose my car.

My PS2 recently went to the giant circuit city in the sky. I'm considering buying a xbox 360 and am wondering if there are any quality racing games out there. I like games that allow you to modify your cars the way that you want to, and cover more than one type of race, I also Liked Juices show off competitions and the drag races, they gave the game a little more variety rather than just driving round and round. So is there any games out there that compare to the GT series or does anyone know if there will be. Oh and please don't bother mentioning GT5 I played it on my little bros PS3 and did not think it was all that great. Sure the graphics are awesome, but it seems they've traded graphics for selection of vehicles and modification options. I love the games were you start out with a used inexpensive little foriegn car. And race your way up to the big leagues, rather than starting out with any car you want and having no real reason to keep on racing race after race.