GPS Coordinate Search For Treasure Sites

I'm making a website that is for logging Treasure sites, and each site has it own GPS coordinate. Like Site#1 has N34'35.3456 W112'45.2345 coordinate and Site#2 has N35'37.3976 W112'44.2265 coordinate and Site#3 has N33'46.3926 W112'49.2855 coordinate. What I need to do is to make a search for sites, by GPS coordinate, that will show up on a list page, that will list all the sites in a radius of 100 miles or so from the entered coordinate, and will list them from the top being the close to the entered coordinate and getting further away from the entered coordinate at the bottom of the list. I have all my sites in a database. So any Ideas PS. I really really like the way that Geocaching.com has there GPS coordinate search.