I really like some of the adult aimed cartoons like Space Ghost Coast to Coast, it takes a little bit of getting used to but once you get into it, it's great! 
Harvey Birdman Attorney at Law - This one I used to hate when I was younger, but it's probably one of my favourite series, it's worth giving a shot.
Aqua Teen Hunger Force - Probably my favourite series right now, more adult than the other two. I absolutely love how psychotic each character can be in certain episodes.
Drawn Together - I really enjoyed the first few seasons, there are some highlights in the later seasons and the movie is alright. The movie for this series comes with a huge warning though, it's pretty morbid sometimes, especially when it comes to kittens and puppies.

Rick and Morty, as previously mentioned, is brilliant.