At the end of each year, our nemesis friendly neighbours at Code Review vote for the best questions and answers from that year. I think that is a great tradition we should steal adopt here as well, because it allows us to showcase some of the amazing content we've created and potentially reward the authors.
2015 has already ended, but I don't see a problem with determining the winners a few weeks into the new year.
To start, we need categories. That's what this post is for! Each answer should contain a category for a challenge or answer to be rewarded. The top-voted categories will then receive separate nomination posts to find the actual winners. (I don't want to put a fixed number of categories here, because I can't anticipate how many proposals we'll get. Something between 5 and 10 seems reasonable.)
Winners will be rewarded with bounties where applicable (that is, for answer categories). For question categories I'm happy to take suggestions for rewards. Maybe our supreme challenge writers like Calvin's Hobbies and Zgarb might volunteer to post a challenge related to the author?
If you're willing to reward the winner of a category yourself (by offering your own rep for the bounty), please mention that in the category proposal.