I really like to look at the articles, issue reports, and research reports coming out of advocacy organizations, think tanks, non-profit organizations, research institutes, etc. You get different perspectives, which can be very helpful. You have to be aware of the *perspectives* of each organization - it may have a particular ideological, political, economic, or social framework that you need to acknowledge in your work. This article (intended for journalists but helpful for academic use as well) provides some useful context for this: Writing about think tanks and using their research: A cautionary tip sheet .
When you end up on an organizational website, be sure to look for tabs named things like Statistics, Research, Publications, etc. to help locate possible information. And always check the About section!
Government publications (congressional hearings and reports, executive agency publications and data/statistics, legal cases, etc.) can be extremely valuable, and are often primary sources. Congresional hearings can often be a good source of alternative perspectives as well .