It really depends on what you like to read/watch

For manga, I'd highly recommend:

-shonen-

Death Note
Yakitate Japan
One Piece
Naruto
Full Metal Alchemist
GTO
Bleach
Love Hina (I put this here cause it's full of fan service -_-)
Ranma 1/2 (can be either, but it has alot of martial arts so I stuck it here)
all Full Metal Panic novels & or manga are all fair game

-Shoujo-

Hanakimi
Fruits Basket
Pita Ten
Hana Yori Dango

-jousei-

Honey & Clover
Nana
Kimi Wa Petto
Paradise Kiss