I've done a few with my kids. I tend to like those that combine use of the GPS along with compass bearings. One of the funnest we did gave even had me find a phone booth, call a toll-free number, and then use information from the recording to get the next bearing.

Ironically that bearing took us to a picnic table on which a young woman was sitting reading with her back to us. At first we didn't notice, but it turned out to be the mother of my daughter's best friend. Her daughter was at the playground playing, so the final leg of that cache was done solo.