This library guide presents a number of different access points to Federal Information on the internet. It includes websites on the three branches of the U.S. Government, an A TO Z list of government websites, an Agencies List, statistical information and more. And if you are not totally satisfied with the way your legislative representatives are representing you, there is a Get Active link area through which you can contact them.
Also, sometimes rather than pinpointing a specific agency that may help you with your research, you may just want to do full spectrum search on the internet. You can do this by accessing the links in the "Good Places to Start" section, or just start by searching USA.GOV.