Well, there are lots of good PC driving games that work fine with a joystick (as they all have setups to play exclusively via keyboard)......the additon of a cheap PC analog wheel will help here but I've played many a Need for Speed game on the keyboard with fine results.
There are also some cool arcade-racer type of games for the PC......Speed Busters and PowerSlide both come to mind (both modern-ish 3D Accellerated games).
Also, the INTERSTATE 76 titles would be awesome.......sadly I'm not sure how well that title performs with modern day videocards...it really wants a 3DFX card as the D3D implementation is....spotty at best.
Then again, a 3DFX Voodoo 2 add-on board will run you about $20 bucks on ebay right now so...

Youc an play mechwarrior reasonably well without a keybaord, but you'll use a lotta keys on your CP.....there aren't any super fighting games on the PC, so I'd recommend instaed you run a PSX emulator and load some of its 3D fighting games (Tekken, Bloody Roar, soul caliber)....
I'm sure there are more........