http://www.trackmanianations.com/indexUk.php
free download, make your own track and race for the top times against other people on the net. The track editor is simple yet pretty flexible once you grasp all the pieces you have available and how they fit together. It's a pretty good racer to boot, the car physics are more than adequate and the gfx are quite nice if you have a high end nvidia card.
here are the couple of tracks I have stayed up late making the last two nights
cheerio speedway:
[Blocked Image: http://marshmonkey.com/cheeriolrg.jpg]
http://nations.tm-exchange.com/main.asp ... 37394#auto
froot loops:
[Blocked Image: http://marshmonkey.com/frootloops.jpg]