GPS Visualizer is a free, easy-to-use online utility that creates maps and profiles from GPS data (tracks and waypoints), street addresses, or simple coordinates. Use it to see where you've been, plan where you're going, or visualize geographic data.
This is the Mac version FizzyCalc. FizzyCalc is an utility that takes coordinate strings in a variety of formats and generates copy-and-paste versions of those coordinates in a variety of other formats. It does high-accuracy distance calculations and projections using the Vincenty Method for calculating distances on an ellipsoid, which are much more accurate than you can obtain from your GPS. It's often used for Geocaching puzzles. Free.
For converting coordinates into various formats: decimal degrees, degrees minutes seconds, UTM, etc