I usually pick something that takes a long time to execute when I need to go exercise. For example, I usually bike for an hour per day when the weather permits. So, I'll pick something that takes an hour to execute. This can be anything, from a kernel recompile, to a php/apache rebuild, to clearing out a gigantic email queue. Sometimes, I'll just write a shell script to execute a bunch of small jobs in a row. That helps a lot.
Also, excellent choice in smiley. You should always try to come off as condescending as possible when asking a group of strangers a question.