FizzyCalc is a Windows application that allows simple conversion of coordinates to various formats. It takes coordinate strings in a variety of formats and generates copy-and-paste versions of those coordinates in a variety of other formats. It also does high-accuracy distance calculations and projections using the Vincenty method for calculating distances on an ellipsoid. These calculations are much better than you can obtain from your GPS unit or most other software out there.

Free street maps for your Garmin receiver. These maps do not support autorouting like the official Garmin street maps.

EasyGPS is the fast and easy way to transfer waypoints, routes, and tracks between your computer and your Garmin, Magellan, or Lowrance GPS.

Tutorial on using CacheMate on a PocketPC for Geocaching.

Various geocaching related search engine plugins for Firefox/Mozilla, including the Geocaching Quick Search (GQS) plugin. Allows quick searches for information from geocaching.com.

GSAK is the all in one Geocaching and waypoint management tool.