Buy TrackMania United on Steam before 02 January 2008 and get it for only $22.45!
This (along with Motocross Madness 2) is the coolest PC racing game made-to-date. Nadeo has done a fantastic job bringing unlimited replay value by creating an easy-to-learn track editor with really cool features.
They even include a Puzzle mode that allows you to have fun while learning how to build tracks.
I highly recommend this game. Go buy it and join FNG for some high-flying, fast-driving, non-stop good times!