There's a new expansion coming out this summer: http://www.polygon.com/2013/3/15/4101742/civilization-5-brave-new-world-expansion
It's $30, like Gods & Kings, and is focused on making the mid-to-late game more interesting with things like revamps of the culture victory, a new lategame "international trade" system, and a new "World Congress" system. The World Congress is the UN of the past Civ games, where you vote on resolutions that affect every player. Of course, there's also the usual array of new civs, wonders, and scenarios too.
I think this sounds pretty great. I like Civ V a lot and I still go back to it, but the parts of the game they're overhauling (especially the culture victory!) can be exceptionally dull. I also missed the old UN, so I'm glad to see that back. What do you guys think - are you interested in this?