Ah! My Goddess

From Dark Horse:

Alone in his dorm on a Saturday night, Nekomi Tech's Keiichi Morisato dials a wrong number that will change his life forever: reaching the Goddess Technical Help Line. Granted one wish by the charming young goddess Belldandy--a wish for anything in the world--Keiichi wishes she would stay with him always! Complications are bound to ensue from this; the immediate first being the new couple getting tossed out of the dorm-it's males only!

As the hapless student and his mysterious "foreign beauty" ride around looking for a new place to stay--risking the different dangers of seeking shelter with an otaku convinced Belldandy is an imaginary woman, and a Zen priest convinced she's a sinister witch--Keiichi's still got his classes on Monday morning! How is his new "exchange student" companion going to be received on the N.I.T. campus? A little too well for normal life to ever return...

Won the Kodansha Manga Award for General Manga in 2009.