Well, I already see most of my suggestions (Planetes, Yakitate Japan) posted. One manga thats missing is
Genshiken, a manga about a manga-anime-video-game college club ("Society for the Study of Modern Visual Culture"). It has some fun characters, and for some reason there aren't that many mangas about college students, so thats another plus.
Also of note are the works by Azuma,
Yotsubato and Azumanga Daioh. Good for their cute humor.