Not sure where it ranks these days, but the Webmonkey.com tutorials got me started back in the day. For instance, in the other thread I mentioned healthcare.gov being built on JSON - they have an excellent "getting started with JSON" walk through with nice, simple examples.
If you want to focus somewhere, I'd focus on modern web technologies. In the old days it was: design a graphical site, convert it to html, make the html dynamic via a scripting server-side language like asp or php, add features via client-side scripting like javascript, and tie it all together with SQL queries on the back end.
Web 2.0 is essentially the effort of breaking that paradigm to allow data to be accessed and traded around by all kinds of devices. That's where the good shit is now. MongoDB, Drupal, JSON, Ruby on Rails, Python, JQuery...
I seriously think anyone with a laptop and a browser could spend 3 months on Webmonkey tutorials (and similar sites) and be worth $100k/year if they have any aptitude for it.