If you're looking for a couple games to play over the weekend for the low price of, well, free-- Here are a couple you should try.
Cubed Rally Racer - Back when this game was first released, I gushed like crazy in our review. It's an isometric 3D racer with completely randomized tracks. You can do all kinds of awesome things like endlessly generate tracks to always have something new to race on, then you can even send those tracks and your associated ghost data to any of your friends via OpenFeint. If you've got an iPad, Cubed Rally Racer HD [$1.99] is also worth checking out because the two player spitscreen mode is really cool.
Giant Moto - We thought Giant Moto had tons of potential when it first was released, but a limited number of tracks and weird controls were hard to overlook. Since then, new tracks have been added along with OpenFeint support for some extra replay value via leaderboards and achievements. If you have fond memories of Excitebike, don't miss this one while it's free.