1. Official Websites
Maru-Ma.com (novels and drama CDs)
Asuka Magazine (manga)
Kadokawa Shoten special Maruma page
NHK Homepage (anime)
OAV Series Homepage (anime)
Presepe OAV Special Homepage
Shima X Shima (Japanese DVD special site)
Web Radio Homepage
Shin Makoku Official Blog
Geneon Homepage (anime)
Funimation Homepage (anime)
Madman Homepage (anime)
HnT PS2 Game Homepage
SMnK PS2 Game Homepage
2. Fansites: Information, Translations, and Scanslations
Kyou Kara Maou @ Newbieguide (seriously, it's got everything)
The Royal Couple
Golden Jade Azure Dream
Kyou Kara Maou Unofficial Reference Guide
Newbie Guide to the KKM Fandom
Kyou Kara Maou Name Explanations (outdated?)
Oresama Quest PC Game Walkthrough
Chinese novel translations
Novel translations by Vivarina
Novel Translations @ Onadoru Euphoria
Some English novel summaries and translations
Novel translation by Pandaberryjam
Novel translation by Niveous_Magics
Lots more novel summaries and translations (thank you tags!!)
Dark Kitsune Scanslations
Aku Tenshi Scanslations
Kurai Ryu Scanslations
Episode summaries 1-78 by kkm_rewatch
Episode Summaries 1-8 by Cinnamon Ass
Episode Summaries 21-41 by thisissong
Episode Summaries 59-78 by kyou_kara_maou Community
Kyou Kara Maou! @ ANN Encyclopedia
3. Fansites: Media
Manga (Chinese) at Sky-fire.com
Novels (Chinese) at Sky-fire.com
Screencaps episodes 1-19
Screencaps episodes 20-42
Screencaps episodes 43-78, 79+, and OAV
Screencaps episodes 1-78 by kkm_rewatch
Screencaps episodes 40-78 by kyou_kara_maou Community
I hate listing these things, so just go here to find them all.
Here are the online dealers that I use to get my Maou fix. I have used all of these dealers before, and would recommend them to anybody. I will not link to a store that I have not personally ordered from, or cannot vouch for.
Kyou Kara Maou! anime goods @ amazon.co.jp
Order the DVDs, soundtracks, and even piano sheet music from this Japanese megastore. Site is Japanese only, but they ship internationally.
Novels by Tomo Takabayashi @ amazon.co.jp
You can find all of the Ma no Tsuku novels listed here. Site is Japanese only, but they ship internationally.
A Maine-based Japanese bookstore that carries the Takabayashi novels, as well as piano music from the anime. Website is in English; ships internationally.
Kyou Kara Maou! anime goods @ CDJapan
Japanese DVDs, music CDs, and VHS tapes. Site is in English, but based in Japan; ships internationally.
Kyo Kara Maoh! @ amazon.com
The good old standby. Order North American DVDs from this online megastore.
I'm often asked, where you do get the magazines that you scan? Well, when I lived in Japan, I could pick them up at my local bookstore. Now that I've moved to Minnesota, however, that's no longer the case. ^^;; I have to rely on online dealers for my magazine fix, so here are a few that I would recommend.
Subscriptions: Sasugabooks.com | AnimeNation.com | CDJapan
Individual Issues: AnimeNation.com | AnimeGamersUSA.com | Akadot Retail