Just came across this: http://www.ibycus.com/ibycususa/
They are actually pretty nice and work with Mapsource just like the Topo and City Navigator products from Garmin. Haven't installed on my GPS yet, but here are some screenshots from Mapsource. The first is the free ibycus map, the other two are Garmin's products for comparison.
Free ibycus map
Garmin US Topo 2008 map
Garmin City Navigator NT 2009 map
So if you don't have the topo maps, these could be a nice no-cost alternative. Also if you have a Garmin auto GPS, like a Nuvi, these would make a useful addition to the pre-installed City Navigator maps. There is no elevation data or contours, but the author says that will come in a later version. I hope so - see his canadian topo maps for an example, they look great: http://www.ibycus.com/ibycustopo/ibycustopo.jpg
After downloading (file contains whole US and takes awhile - over 3 hours for me), just run the installer. Then start up mapsource and you can use them like any other Garmin map. But be careful if you already have the topo maps on your GPS, installing these might wipe it out (on the GPS, but not on the PC). For a lot of discussion, see this long thread: http://forums.groundspeak.com/GC/index.php?showtopic=189762
They are actually pretty nice and work with Mapsource just like the Topo and City Navigator products from Garmin. Haven't installed on my GPS yet, but here are some screenshots from Mapsource. The first is the free ibycus map, the other two are Garmin's products for comparison.

Free ibycus map

Garmin US Topo 2008 map

Garmin City Navigator NT 2009 map
So if you don't have the topo maps, these could be a nice no-cost alternative. Also if you have a Garmin auto GPS, like a Nuvi, these would make a useful addition to the pre-installed City Navigator maps. There is no elevation data or contours, but the author says that will come in a later version. I hope so - see his canadian topo maps for an example, they look great: http://www.ibycus.com/ibycustopo/ibycustopo.jpg
After downloading (file contains whole US and takes awhile - over 3 hours for me), just run the installer. Then start up mapsource and you can use them like any other Garmin map. But be careful if you already have the topo maps on your GPS, installing these might wipe it out (on the GPS, but not on the PC). For a lot of discussion, see this long thread: http://forums.groundspeak.com/GC/index.php?showtopic=189762