Biseinen.com
Dedicated to the ever popular "Beautiful man" in Manga, it features shoujo, shounen-ai/yaoi and fan works.
CenterStorm Online
Project maintaining several improvisation rounds. Information on participation, archive and forum.
Improcomics.org
An online community of amateur webcomic artists participating in impromanga projects. Genres include action, comedy, and romance. Also includes member pages, greeting cards, and forum.
Impromanga World
A place to go if you don't just want to read a manga but help to create a manga.
MK Impromanga
Currently featuring the impromanga Power Force with more planned in the future.