Polarbit released Raging Thunder 2 a while back -- it's the sequel to their App Store launch title that's serving up solid racing on both the iPhone and the iPad. It's not the best pure racing game out there (Real Racing HD has gotten exposure, even in Apple stores, for that), but Raging Thunder has quite a bit of fun and depth added to it, allowing you to upgrade cars and even go for some Burnout and Mario Kart-style arcade action. And the latest update to the title, released about a week ago, adds online leader boards and touch controls for racing (in case you don't want to tilt your iPad or iPhone around as you play).
Raging Thunder 2 is definitely a respectable racing title, especially good if you're an arcade racing fan, and the price is just as temptingl: US$2.99 on both the iPhone and the iPad. If you're in the mood for a little action with your racing, and a deeper experience than some of the pick-up-and-play racing titles, Raging Thunder 2 is worth checking out.