These are official and unofficial sites for the shows Buffy the Vampire Slayer and Angel, the Series, as well as for some of the actors on each. This is by no means an exhaustive list, simply the ones I like and find useful.
Buffy's Official site
Buffy Cross and Stake
City of Angel
Sarah Michelle Gellar.com
David Boreanaz, UK site
These are sites which may be helpful to those who wish to write for the Buffy fandom, and places where one can post stories. This is not an exhaustive list, just the sites I like right now. This page is subject to change and update as my interests change.
The SanctuaryFor all things Angel. GREAT site
Buffy and Spike Diaries Good resources, just scroll past the Spuffy stuff.
Obsidian Moonlight Writing link at the bottom.
The Buffy timeline
Canon Vs. Fanon
BtVS Writers Guild
All things Philosophical on Buffy the Vampire Slayer and Angel: The Series