How do you volunteer professional services?

keefus_a writes: My wife and I usually take a week long vacation in the Spring and I tossed out the idea of volunteering abroad. Neither of us has a problem with doing manual labor, or whatever task is needed. However, I thought it might be of some value, and substantially more rewarding than our daily grind, if we could volunteer our professional services (I'm a network guy and my wife has a master's degree in counseling). The problem is that I haven't found any resources for doing so on a short-term basis. So I ask Slashdot. Has anyone ever done short-term volunteer work in your professional field? What organization did you contact? Or are we better off donating money to a particular cause and just working on a tan?