There are a large number of question and answer sites out there, but very few which provide good answers. The ones I have found that tend to provide good answers are as follows:

StackExchange Network (including StackOverflow) Ask MetaFilter Quora Reddit (on particular sub-reddits such as Ask Science, Ask Historians, Explain Like I'm Five and sometimes Ask Reddit)

Are there any other question and answer sites out there with a high quality of discussion? I'm quite surprised that I haven't been able to find any newer entrants - it's actually easier for new question and answer sites to have a high quality of discussion