Haven't played much but my nephew seems pretty hooked on Contract Killer (fps)
Now for a free racer, don't think there is much out there to rival the better paid ones. I downloaded GT free+ HD from Gameloft but so far it hasn't gotten more than 5 minutes of my attention so can't really judge it. But on first glance it seemed mediocre. Again, ridge racer is free, however I wasn't really a fan of game back in the day. Would love for SEGA to port Daytona to ios.
Some good free games I got on my new iPad :
Temple run, very addicting but I'm sure the controls deliberately bugger up so you miss-jump!
Homerun battle 2 is cool for a quick time waster. So is circus pain.