There are hundreds of databases to choose from, but these three offer good places to start:
Academic Search Premier (aka EBSCOhost Academic Search Premier) -- access to 8,000+ journals & magazines, many of them full-text online [Tutorial]
Academic Universe (aka Lexis/Nexis Academic) -- the best place to look for articles from thousands of newspapers [tutorial coming soon]
CQ Researcher -- non-partisan, comprehensive reports on topics in the news tutorial
If these databases do not provide enough information on your topic, it is always a good idea to talk to a librarian to get recommendations for other databases to try. It saves a lot of time in the long run! Learn more about choosing databases with this tutorial.
NOTE: If you already have a citation for an article, you can skip searching a database and use the Citation Linker tool instead!