Add your must-have subreddit here so people can vote on which is the best.
http://www.ranker.com/list/what-are-some-must-have-subreddits-/aegeus,
http://www.reddit.com/r/spaceporn
http://www.reddit.com/r/spaceporn
http://www.reddit.com/r/depthhub
http://www.reddit.com/r/radioreddit
http://www.reddit.com/r/FoodForThought