SuperTuxKart is the classic open source racer and it has a brand new version with new tracks. This is the first RC release that will become a major new release.
The new release features three new tracks, an a new audio track, recording your times and playing against ghost replays. Font handling now supports TTF fonts and they also added in AI for the 3 strikes battle and soccer modes.
They are also making progress on the network features which have been highly requested. They are making progress on LAN support, but it's not where they would like it to be yet. Sad that they haven't finished it yet, but still a pretty nice release.
I can certainly imagine the game being more popular if it had properly online gameplay. I know it would be fun to play it with a few of you.
You can find the code on github.