Holy smoke so many good suggestions around here and nobody is going to talk about Attack on Titan? I really recommend it, it's my all time fav anime and manga too (even if the manga doesn't have an amazing art, it still looks amazing and right now it is on fire). If you plan on watching it, i would suggest to not read the manga at all, only if you can't resist anymore until all the shit from manga is animated, but you will ruin your experience if you read the manga before.
I tell you this from my own experience, i started reading the manga because the anime was taking too long to be done, but tbh right now i regret so much, because i can't image how my experience would've been if i hadn't known anything at all from the manga.