Let me mention three good sites.
The first is a shameless plug for
my own site. I have Buffy summaries from Seasons Four and Five and will soon be posting Season Six. I try to capture the feel of the scene and how the characters seem affected by events more than repeating the dialogue - kind of a synopsis. I also have a collection of trivia quizzes.
For dialogue, like finding the episode that your Spike quote was from, I use
Psyche: Buffy Transcripts. It contains all the dialogue and lots of the facial expressions and reactions. It's the source I use to get a quote EXACTLY right.
For star info, I rely on
The Internet Movie Database. It is the best source I have found for factual info on movie and TV personalities - what have they starred in before, their birthdate and location, new projects, etc.