Get Memory-Map Navigator (
www.memory-map.com). The new version lets you use the free maps you can download from the USGS server or the TerraServer via the USA Photo Maps tool. Here is a link that explains the steps needed to do it:
http://www.memory-map.com/index.html...s_seamless.htm. The link talks about aerial photos, but you can also get topographic maps from both location. If you want aerial photos, go for it. I normally use topos though, because they are much smaller. Memory-Map includes a PC version and a PDA version. The PC version is more powerful, but I have never used it in the field. I do use the PC version for planning before I leave and then transfer routes, mark and maps to the PDA as needed. I guess if you wanted aerials, you could always take a laptop with you.