Common: general things that appear to be common across a lot of anime.
Gasaraki: Gasaraki notes
An ADV site with memos, synopsis, interviews, image gallery and trailers. These are meant to supplement the DVD extras. The ADV web page is gone or relocated now.
Kenji Miyazawa: His life is outlined in Spring and Chaos, Night on the Galactic Railroad is based on one of his writings of the same name, and They Were Eleven was based on one of his writings as well. Go here to see "The World of Kenji Miyazawa".
Lupin: Lupin the Third . com
Looks like an interesting fan site, any questions concerning the Lupin shows should be directed that way, it looks like there is quite a wealth of information. A fan run site.
Miyazaki & Takahata works: Nausicaa . net A fan run site.
Nadesico: Translator's Notes.
Urusei Yatsura:
Tomobiki-cho A fan run site.
AnimEigo's UY Liner Notes, eps 1-10
AnimEigo's UY Liner Notes, eps 11-20
AnimEigo's UY Liner Notes, OVAs
AnimEigo's UY Liner Notes, Movies
The links above are extensive resources on the show, I feel it is futile to try to add any more.
Witch Hunter Robin: The Maelifica Compendium extras on the Bandai R1 DVDs provide more background information than I ever could. Be sure not to read too far ahead, they seem to provide potential spoilers.