My absolute favourite is Baccano!, because... well, just go watch it.
Runners up are:
- The Melancholy of Haruhi Suzumiya, for being absolutely hilarious and having one of the best subtle romances ever
- Full Metal Alchemist: Brotherhood, for being 'epic' in the truest sense of the word
- Black Lagoon, for balancing an insane amount of kinetic energy with just enough character development to make you give a damn
- Welcome to the N.H.K., for being brutally honest and at the same time disarmingly sweet and funny
- Neon Genesis Evangelion (new addition!), now that I've (finally) been able to reconcile the ending to myself.