Compulsion: Yami no Matsuei
My fave site - so much so I visit it daily :) Flash comics of recent issues of Hana to Yume, FANFIC, high-quality scans of the calendar and so much more! Has a wonderful list of links - 50+!

The Gushoushin's Library
Loads upon loads of information & images!! A must visit. This is where I first learned about Yami.

Theira.net
A bit of everything is found here - anime, manga, loads of scans and info. Best part: Translations! Both the series & sections from Hana to Yume. Also found here: movie clips :)

Within the Darkness
Screencaps from the first few episodes and the beginning of episode summaries! Lovely layout as well.

Lunatic Angel's Descendant into Darkness
Chinese site but has some of the BEST fanart I've ever seen in "ROOM 003". I keep getting a "forbidden" message, but maybe it'll work for you.

PaperThin Pleasues
Beautiful layout and some scans from the artbook! Very clever and pretty site. If only mine looked half as nice ~..~

The Genki Shinigami

Tari has his own fan club so check it out!!