Official:

Hora
http://www.ka7.koalanet.ne.jp/~godsynth/

Schwarz Stein
http://midi-nette.com/midinette/ss/

Related:

Kaya
http://rose.cage.to/

Mine:

...and I guess you can have my banner too,
just cause I think it's cute.

Unofficial (Fan-made):

A very lovely Kaya fansite that makes this one look...well...not cool ;_;
Discography for Schwarz Stein here.

(ps. I did the translations)

Red's site with gallery, fanart,
and everything Hora related that was not on here.