Per this post and Westeros.org’s Compendium of Theories, I’m going to try to come up with a list of theories from/r/asoiaf. No disrespect to Westeros, but this subreddit does some amazing theory development and analysis that is worth posting here. I’ll start with some major questions and theories and then do a hodgepodge of miscellaneous but highly upvoted theories. I’ll close with a tinfoil category.
Obviously, everything below will be spoilers. So, please be aware that even the theory titles I gave are spoilers.