Harem manga and anime are so popular that they have their own category. It's easy to name a few: Girls Wild, High School DxD, Sekirei, The World God Only Knows.
Why is this such a popular theme in both anime/manga? It is odd because in fantasy literature, American cinema, and Western television, harem is not a common theme and would offend most. How is it that they are so extremely prevalent (and seemingly accepted) in anime/manga?