Auto Club Revolution open beta is go, race for free
There aren't a great many free to play racers out there. If Need For Speed World's reliance on single-use power-ups puts you off, and Trackmania's spiralling tracks feel a little too mad, you might want to try Auto Club Revolution. It's just entered open beta, which means you can sign up for an account, download the tracks and start racing for free.
As you race you can unlock new cars and tuning options, and there's a fairly decent car customisation suite that will let you decorate your ride with decals and new paint schemes. It's made by Eutechnyx. who developed last year's official Nascar game and, before that, Ferrari challenge, so don't expect any giant blue shells or homing rockets in this one. You can sign up and start playing on the Auto Club Revolution site.