Wow, the internet is full of documentation. If you go back to the roots of the world wide web, people like Tim Berners-Lee and before him even Ted Nelson with project Xanadu (and go back to the Manhattan project with Vannever Bush it isn't a new idea at all) the idea was to share information. Learning material, instructions and books could all be connected.
This blog is all about sharing and linking. This is information I have gathered either professionally, or just as part of learning something else. Certainly as a pilot, I have had to learn some of this, but the theory came probably years before as a kid getting my ham radio license, or building my first robot. I sometimes paraphrase other documents, and even copy stuff here from other places.
The greatest source of verified information I share is from wikipedia. I may know something about something, but I usually try to verify it with some other source, and searching Google will usually point me at an article in wikipedia.
The math help I get from the aviation formulary web site. I don't know Ed Williams, I'd love to meet him. I have used his site for years and years writing aviation software. This is well presented, and detailed or not as necessary. This site focuses on the math, and that is all. Good stuff!
For charts and routes, I tend to rely on SkyVector.com. I can't believe this resource is free, and I appreciate it. Flight aware has plates and ASDI data, so it is also useful, similar but different. For airport information, I use Airnav, which has links to other sites including vfrmap.com and FAA's pilotweb.
Weather needs are met by the NOAA ADDS web site. There is so much information here that the weather channel, weather bug and other weather sources make really hard to look at. If you want to really forecast what will happen on your route of flight, ADDS is the only source.
Buying and selling of aircraft and parts, I rely on Barnstormers.com. The baroness runs a great web site, and I get the weekly email. I can't not mention Trade a plane, since if I were to sell my plane, I would list it on both sites. I still like the physical paper of trade a plane, but right now I am not subscribed. I also shop ebay for some aviation items also. For building supplies Wicks Aircraft, and Aircraft Spruce are the main sources.
There are several resources for electronics concepts. For builders Bob Nuckolls Aero Electric Connection is the main place. If you want to build your own avionics, there is a page dedicated to homebuilt avionics.
These are my go to pages, what are yours?