GPSFileDepot seems to be a great resource for U.S. and other maps. I just downloaded maps for Washington, Idaho and Montana and loaded them onto my GPS and they seem pretty good.

One thing I noticed is that the maps don't all come from the same provider so they may not all line up exactly. For example, with the maps I loaded, there seems to be an 800 meter or so area of missing topo information between Idaho and Washington.

Oh, and all the maps (Ibycus and the GPSFileDepot ones) can be loaded on to Garmin devices using Garmin's free BaseCamp software.