Projects For When You Have Too Much Computing Power?

Spackler asks: "Recently, I completed a consulting gig that I needed to pick up 5 fast machines for a data conversion. Now that the conversion is complete, I have all this hardware, and nothing to compute. I know I could toss them together as a Beowulf cluster, but the big question is, what types of things do I compute on them? I know distributed.net, or Seti@home, or GIMPS would like them just added in, but are there any cool off the shelf things that need a ton of power, and take a long time to process, that can be done on a normal cluster? Some odd (but easy to understand) math question? Something cooler than brute force encryption breaking?" We've already had a discussion on some of the more well known distributed projects already, what are more home grown projects that one can use a cluster for?