If you need a new weekly manga, Nanatsu no Taizai (Seven Deadly Sins) is somewhat fresh, it's only at 56 chapters so far. I'd also recommend Hunter x Hunter and Berserk since they are ongoing (frequent hiatus though..)
If you want series' that have ended but are still long, check out Yu Yu Hakusho (all-time fav of mine), Katekyo Hitman Reborn!, or for a manga (sadly no anime) 666 Satan (O-Parts Hunter in US) which is written by Masahi Kishimoto's twin brother. It's very good, but much much shorter than Naruto.
Hope I helped, good luck with finding a series you enjoy.