This is one of the most popular manga/anime in the world. The comic and cartoon is still on-going in Japan, a testament to it's popularity.
One Piece is a story of a boy, Luffy D. Monkey, and his ambition to become the King of all pirates. Along his quest he meets different people--a skilled swordsman/bounty hunter named Roronoa Zorro; Nami, a greedy thief who has a knack for navigation; Yusop, a great liar who has an affinity for inventing; Sanji, a bad ass warrior cook; Chopper, a sentient deer who is also a skilled physician; and Robin, former member of Baroque Works.
Together, the gang sets sail to unknown seas in Grand Line spelunking into high adventure in every turn.
On another note, the debates in the web between Naruto fans and One Piece fans are absurd. The two are both Shonen but everyone can enjoy both series without fighting which series is better.
Anyway, if you want to read the manga of One Piece, just use my search box to find manga scanlation links.
Go here and here for One Piece manga scanlation links.
