I know there are already a few posts on this, but they've been dead for awhile now. Anyways I recently read that GeoCaching turned 10 years old and looked into it a little while it's kinda geeky it's also pretty fun.
This is what I'm currently using
http://www.nicque.com/PQz/GCz.htm
It ties directly into
http://www.geocaching.com/ and Google Maps.
If you've never heard of it watch the video on the GeoCaching home page and then get ready to go spelunking.
Also if anyone else is into GeoCaching what applications are you using?