Open access repository of general GIS spatial data?
I'm brand new to GIS programming so please excuse my lack of knowledge.
I am developing a GIS web app using MapGuideOS to host raster images (base maps?) and PostGres for some vector data. I've been reading a lot of documentation and books but some things are still a little confusing...
Where can I get some free base maps for the united states (Does that mean I need shapefiles)? I want to host something similar to the basic view of google maps (state boundaries, county boundaries and roads), but only for the United States. I know I can use google maps and draw my vector data on it, but I would like to explore options for hosting it myself, before I commit to GoogleMaps/Bing/Yahoo.