Shaded Relief – Home is an excellent place to start. Natural Earth has nice data and, as was pointed out, there are many 3D and contour resources available from the USGS web site.
http://www.shadedrelief.com/plan_obl...an_oblique.pdf has good information on the sort of things that you're trying to do, if I understand correctly.
Cartography and Geovisualization Group, Oregon State University has useful resources as well.