Haruhi is a poor tomboyish student at a school for the wealthy, which she was only able to attend because of a scholarship. Looking for a place to study, she enters a music room, only to find that it's being used by the Ouran Host Club. The guys of the host club intentionally play up their attributes to please the customers, which even they realize is silly, but it does work like a charm. Haruhi thinks it's all ridiculous, but before she can leave, she accidentally breaks a vase. She can't pay for it, so she's told that she'll have to stay and do odd jobs. She does this until they realize that she would be more valuable as a real member of the club. Not realizing she's female due to her appearance, they fix her up and give her a male uniform. She makes such a handsome boy, they decide to have her keep up the charade even after they find out she's a girl. Although she thinks the guys are crazy, they seem to be good people, and not having much choice, she plays along.
Info taken from AnimeNewsNetwork.com
My personal thoughts: I like this series. Although the drawing and art are bishounen type anime as it's derived from it's manga, the story is very nice. Romance stuff plus comedy. So far I can say, it's a good anime. But I haven't read the manga, so I couldn't give any impression for the differences between both.