We don't often talk about Adventure Time around here, partially because we assume you're already watching it. If not, here are twenty reasons to watch it.
Adventure Time is essentially a Dungeons and Dragons cartoon as written by players instead of cartoon writing staffs in the '80s. The show has a fairly silly surface, with animate candy people and a kid hanging out with a slacker talking dog, but the show has a rabid fan base for excellent reason: Towards the end of the third season, the show starts exploring the history of the Land of Ooo and since then has revealed a lot more about several key characters. It's not afraid of getting dark.
Also, it's funny as hell, and thus excessively GIFable. See for yourself: