Here are the sources I use/am aware of: United States/~40km of Canada North of the border, including Oahu, Puerto Rico, and American Samoa and all 48 of the Contiguous United States: (GeoTIFF Format): USGS EarthExplorer United States, American Samoa, Maui, Kauai, and Maui Volcanic Chain, as well as certain USA Protectorates (GeoTIFF in some areas, JP2 in others - JP2 requires conversions): TheNationalMap Many cities and areas provide TIFFs of their areas. Please note that G2XPL is illegal if you are making use of Google, Bing, or Yahoo! imagery, along with copying any Google data (including image data) into WED. (edit:) This includes using Google, Bing or Yahoo! imagery as a reference material. No derivative works as per the terms of use. Cheers! I hope my sources helped you out. If you need help using them, I am familiar with the tools.