There were several that sucked me in:
Love hina, good story line, lots of funny and the manga actually put a real finish on the story of the series
Ai Yori Aoshi: A way beyond awesome story, the art work was amazing and it actually made me care for the characters well being
Full Metal Panic: I actually prefer the Manga over the anime series, even though the English translation has only covered up to the end of first season of the show (And it included a good portion of Fumofuu as well). Can't wait till ADV gets up off its ass and finishes it.
Cardcaptor Sakura. What can I say, I read it on a dare from a friend, and I actually enjoyed it. The manga had a lot darker theme then the show (mostly because Nelvana mutilated the series). I really do believe that the women at clamp have a thing about inappropriate Child/Adult relationships...
There are others, but they are just too many to list here.
Also, for future reference:
If you ask for someones opinion, give your own first.