You can unlock two other cars by completing the Challenges section. I've been playing mostly Time Trials in Arcade mode using the Corvette, it's fun doing mindless laps while watching TV and trying to beat your best time. Here's the current City Short Circuit / Arcade world leaderboard, I'm still trying to find that extra 0.9 of a second that will put me in the top 3 hahah!
Thanks for the tip, Vic! I haven't really spent time learning the game coz I'm still caught up with another multiplayer game.... Will try what you said...