Ok, here's the first listing of the Harem. Part 2 is in the works, you all can suggest whoever you want, almost every female character in the anime/manga/light novel is able to join the harem.

1) Rias

2) Akeno

3) Koneko

4) Asia

5) Xenovia

6) Irina

7) Rossweisse

8) ??? (Your Familiar)

Don't forget, you can still suggest characters for the Harem part 2.