I've bought or (mostly) rented quite a few racing games, but haven't found any as good as GT3. But here are a few brief, very biased impressions.
WRC: Pretty good, but it's too easy, I think, fairly short and--while it does have weather--it doesn't vary (ie, it's always raining in the same stages). This could have been a great game with a little more work.
Tokyo Extreme Racer Zero: I was going to rent it, but for $20, I bought it. I really don't see why so many love this game. It's streat racing, yeah, and the highway system is pretty big, and you get stickers, etc... But it's really heavily an arcade game with some absurd speeds, not much for real-world physics, etc. RWD cars oversteer and FWD dos plow a bit, but it's not so much real as it seems the developers going, "Look! We put understeer here and oversteer there! Whooee."
F1 2002. Got one for the PS2. It's pretty good, but I had an earlier PC version (at a massive discount) which was better. Check it out if you like F1, but preferably on the PC. The coolest thing for me is that you get all the F1 tracks and it's fairly realistic. Also, unlike even GT3, miss a breaking point and you pay for it dearly.
Ridge Racer: rented it; hated it.
CART Fury: Rented it and believe it's the most horrendous game I've ever seen.
Test Drive: Had a pretty old PC version. I wasn't impressed and haven't tried out the series since.
Need for Speed: Have the Hot Pursuit version for PC. It's arcade, but I somewhat enjoyed running from police before getting a PS2 and GT3. Haven't played it since.
Grand Prix Legends: Have been looking for it; can't find it.
Moto GP2: Yeah, motorcycles. I rented this not long ago. The replays and graphics, at first, look nice. Approaching GT3, even, but they're not quite there. There was something oddly artificial about it, I thought. But the gameplay was generally good but seemed somewhat short. I'd recommend a rental if you like motorcycles, anyway. I don't plan on buying it.
MX Freestyle. Eh. It's ok. Not knocked out by it. Maybe a rental, not a buy.