For the past couple of days, SEGA has been running a mini sale on some of their iOS games, giving away Sonic & All-Stars Racing Transformed and GO DANCE for FREE. Plus they have some nice discounts on a few of their other Sonic (and non-Sonic) games as well.
I have no idea when the prices will be going back up, so snag these deals while you can.
Note that App Store prices fluctuate frequently and there can be some propagation delay, so the prices above may not be correct. Always make sure that the price is correct before clicking 'BUY'.