I use StackOverflow as much as anyone when I am looking for the answer to a specific question/problem, but when I'm looking for a deeper description of a topic or approach there are usually better places to go. And sometimes I'm just looking to see how other folks do things and why. Not just to solve today's problem, but to add tools to my toolbox. You can never have too many tools, you just need to know when to use them.
The first few are very active, while the latter are more static, but still have a lot of useful info and current comments. Enjoy these and add your favorites in the thread.