SuperTuxKart 0.4 is being packaged as we speak. Eventually (although not yet as of time of writing) they'll be up on Sourceforge. It goes from being quite a naff game (STK 0.3 was basically TuxKart with better graphics, and TuxKart has some serious gameplay flaws) to being really quite a good game. Now it is a bit of polish and some better tracks away from being a great game. I suggest you try it out, the improvement is massive, and if 0.5 brings the same level of improvements as this release, then STK 0.5 will be a very good game indeed.
There's a bit of competition around the corner though. Platinum Arts Sandbox 2.1 was released. This is a sandbox game aimed at kids and this version contains a kart racing mode so kids can build their tracks in the very easy Sauer environment (PAS is a Sauer derivative) and then race on them all without the game without specialist tools or knowledge.
Word War vi (that's vi as in vi vs emacs as opposed to VI as in 4 6 (d'oh! dang roman numerals...)) is a side scrolling shooter which is, well, kinda geeky but also kinda fun. (Did you spend a few secs thinking "World War IV" too?)
In case you didn't guess from the title, there's no screenshots in the post. I'm too busy to do it today! Edit: Ok, thought I'd post this Word War iv vi video since it's kinda cool: