Honestly, a lot of my initial information on a subject I'm not an expert in comes from Wikipedia and Encyclopedia Britannica.
While usually not as in-depth as Wikipedia, Encycopedia Britannica has a ton of useful information.
By David Woods, Ken MacTaggart and Frank O'Brien
The Apollo flight journals are a facinating and in-depth look at the Apollo missions. They contain transcripts of the air-to-ground comm loop, the PAO comm loop, and in some parts, the converstions amongst the crew. Accompanying this are explanations and notes by the authors, photos, video of TV broadcasts, and audio recordings.
History.com has some good outlines on certain topics and is a jumping-off point for deeper research.
IEP is a peer-reviewed online resource of philosophical subjects and key figures hosted by the University of Montana.
Includes a description of navigation techniques of the polynesian seafarrers.
Raw transcript of Apollo 11 voice transmissions.
A history of the vegetative state.