If you want to get some good info look at this.

Characters

Complete Heroes Story, Shadow, Rouge, Cream

Complete Babylon Story, Silver, Blaze, Eggman, (a robot that is a sample like E-1000000R in the previous Sonic Riders)

Gears

Angel * Devil: Complete Babylon Story (This gear is a mystery gear I don't know what it does, when you get enough rings, you have to gamble Yellow is Angel and Purple is Devil, Devil is bad and Angel is good I think I'll try to find out, check out gear gallery in EXTRAS for description, maybe you can find out!)

Stories

Babylon Story: Complete Heroes Story