National Geographic has released TOPO! version 4.5, adding support for Garmin Oregon, Colorado, Edge and nuvi models. A Mac OS X version is also available. This is a welcome improvement, as too few mapping software programs support these models.
EDIT: The update allows transfer of data only, not maps. See the comments at the end of this post for more details.
While there are other great mapping programs out there, TOPO! remains my favorite for generating high-quality printed maps to go with me into the field. My normal practice is to transfer waypoints and tracks to TOPO!, and overlay it with a UTM grid for easily referencing my position.