Two projects that I have on back burner right now (too busy with work) are a fractal/coherent noise Perl module that I occasionally rant about on PM, and an L-system based random building modeller. Thanks for reminding me.

The first Perl project that comes to mind as concise and satisfying is a little script I put together to play around with influence maps (poke around on http://www.gameai.com for more info on these). I had it working inside twenty minutes, and it was cool to see my assumptions being shown right. A few weeks later I came back to it and added more knobs and switches, and spent more time playing around with it. Maybe one of these days I'll use it to write a basic GEV player.