The popular Ah! Megami-sama manga by Kosuke Fujishima follows the story of a hapless college student named Keiichi who accidentally calls a goddess named Belldandy down to Earth. It has several forms in anime, including a five-part OAV, movie, and a rather unique television series. With 48 episodes of about five minutes each, the series focuses on the goddesses in their "mini" forms, where they are able to shrink themselves and still get into trouble, particularly with another hapless character, a rat named Gan-chan. AMG isn't really shoujo, but I've made an exception. :)