Official sites
Ér official homepage
GAIA no gensou yoru - Hinako's official homepage
Hinako's blog
Unofficial sites/other
Connection - unofficial fan page with many live photos, etc.
Ex Orient Lux Ér - another unofficial site. Doesn't apear to be updated.
DEAD SILENCE - music unit featuring Hinako

NB: Most of these sites are now defunct, but old copies may still be viewed via the Internet Archive.