Get One Piece. Be sure to get the Japanese version. IMO the english voice overs are horrible and using some rap song for the opening is just meh >_>
And get Hajime no Ippo (about boxing), Prince of Tennis (about tennis, duh), Shuffle!(love, romance, comedy), Azumanga Daioh(comedy, school), Fate stay/night(hero spirits, pwnage).
EDIT: + Gungrave(Dead guys, shooting, romance, loyalty, mafia), Full Metal Panic(comedy, school, mechs, army), GetBackers(comedy, fighting), Ah My Goddess(godesses, comedy, chunk of life), Shakugan no Shana(school, comedy, sword fighting, spirits), Cowboy Bebop(space, shooting, stealing, comedy), Eyeshield 21 (american football, comedy), Air Gear (roller skates, comedy, leadership), Fruits Basket (comedy, romance), School Rumble (comedy, school), Hikaru no Go (a game called go, comedy and a soul).