Here's my complete list of manga and anime with *star* ratings (5 being the best) so far... subject to change/update. Hope you find it helpful, feel free to comment and suggest anything you like that you think I would enjoy as well!
Code Geass: Lelouch of the Rebellion
Manga: The only related manga I know of is "Knightmare of Nunally", I checked out the first volume and really wasn't that impressed, this is probably because Knightmare of Nunally is set in an alternate universe from the anime, though. Due to my incomplete knowledge of the series, I have no rating on this. If you know of a manga based on the anime, please let me know!
Anime: