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.
Viewing MrSid Imagery With qgis
I recently used the OSGEO4W installer to install qgis on a new laptop. I was really surprised how easy it was to get qgis up and running with all the options that are fun to have. Here is a desrciption of all it features from the qgis website.
This is the MSVC based build of QGIS. All dependencies are supplied via the OSGEO4W installer, including python, gdal (including MrSid and ECW Wavelet compressed raster support) etc. This is most suitable for people who have fast internet connections and who want to be able to update dependencies from the OSGEO repository easily.
I had no problems with the installer and love that i can view mr sid imagery along with other data. I think that this was one of the last features that open source GIS packages needed to be highly viable.
Free Wyoming GIS Data
I do a lot of GIS work in Wyoming and have found that the there is a great amount of GIS data available for free. The Wyoming Geographic Information Science Center is a great resource if you are looking for GIS data for the sate. Their data services include the Wyoming Geolibrary where you can browse data sets by scale, theme, or project. But the best way to download the data is from the WyGISC Data Server which allows you to interactively view and then clip the area that you are interested in and download the data.