My number one favourite https://www.qoura.com
I have learnt so many incredible things from Quora I'm a huge fan
2nd on the list is http://www.nairaland.com
Believe me, as a Nigerian, the comments i read on this blog makes me laugh so hard that i can't miss visiting it daily.
Last but not least is https://www.wikipedia.org
Indispensible to me for getting my facts right, adjusting my study notes, learning new stuff,....
Those are all great sites. Good contribution to the contest.