United States government agencies have a large number of maps available online. As well as general maps there are many that cover specific topics and data that has already been prepared and is readily available to download or print. Maps cover a wide variety of characteristics, not just geographical but also political and economic amongst many others. One of the great features of these maps is that they can often be customized, so you can create maps that show exactly what you are looking for, allowing the combination of different layers.
To find the maps of the United States Congressional districts: