@stevetheradroach: I'll let others do all the more in-depth of why Kreia is this beloved kind of character, but at least for me it's the pure philosophical difference that she brings to the Star Wars universe. In all of the films and expanded universe, there just isn't a character that brings the observations of both sides to the table quite like Kreia, and than disputes them. Jolee Bindo would be my close second.
I do remember one cool moment with Kreia where on Dantooine (I think it's when you come out of some cave from a quest) and you're confronted with some bad guys. It's a pretty usual circumstance where if you go light side, she bitches you out. Go dark side, she tells you to go get fucked. But pick the option that circumvents the usual and you end manipulating both factions to your bidding and she applauds you and praises you. That Kreia, she likes to talk and berate and everything, but she is a teacher at heart. Go with options that are more in the middle, or manipulative, or don't conform and she sees you as a student that gets it. Any means necessary without conforming to one moral philosophy or the other. I really like Kreia. Even if she tells me to fuck off a lot.