If you haven’t yet visited the Wikipedia page for Shakespeare, I highly recommend it. It’s not like you’re going to find any new information that you couldn’t find anyplace else. But here it might be better organized than anywhere else. Who knew about the “questionable” plays? I knew about the existence of Cardenio, which is more “lost” than “questionable”, and The Two Noble Kinsmen, which I got into an argument with my neighbor about (I lost, arguing “I have several copies of the complete works and there ain’t no Noble Kinsmen in it!”) I’m talking about plays like Edward III or Sir Thomas More, two plays which scholars think might have been collaborated on by Shakespeare.
Of course the entry itself is link-heavy enough to keep you interested in pretty much any direction you wish to go. Elizabethan history? Shakespeare contemporaries? The actual text of the plays? All there.