For a recent project I needed to get some Montana GIS data. During the search I came across the Montana Geographic Information Clearinghouse. The clearinghouse has GIS data sets that you can download for free, such as topo maps, digital elevation models, cadastral data, aerial photographs, and NRCS soil data. They also have a handy tool called the GIS Data Bundler that allows you to choose multiple layers and have them clipped to a geographic area or buffer. Another great service they have is the NRIS Raster Image Service which allows users to connect directly from their GIS software. Check it out for the imagery available and how to connect to their server.