BtVS still counts as one of my favorite franchises. I've got quite a few of the DVDs, I've bought several of the tie-in novels (I especially recommend the Tales of the Slayers series) and a few of the comics (though I dropped Season 8 fairly quickly in).
I've also purchase Eden Studios Buffy the Vampire Slayer RPG. Originally released in 2002 (if memory serves), this game and it's various sourcebooks (and it's sister game, the Angel RPG) really capture the flavor of the show and setting.
The system uses a modified version of Eden's Unisystem, referred to as the Cinematic Unisystem. The game offers a lot of options; using the original corebook (which covers up to Season 5; the Revised Corebook, which you see a link for, covers up to the end of the series), you can make Slayers, vampires, robots, witches, and more. It also allows for Xanders and Dawns to stand alongside superpowered Buffys and Spikes and hold their own.
Actual gameplay is incredibly stream-lined; most things are resolved with a D10 roll added to the score of attributes or skills. And that's for the players- GM's have things even more simplified as the NPCs have pre-rolled stats; a flat number (I want to say six) is added to the existing scores so the GM can prep ahead of time.
The sourcebooks add quite a bit too. The Slayer's Handbook is a grab bag of options (making the title a misnomer, as there's not a lot of specific Slayer info); Monster Smackdown adds a whole lot of NPCs with a few options for monstrous characters; The Magic Box expands the rules for magic and adds a few other paranormal options; and there's a few other features in Eden Studios Presents, a magazine for all Unisystem lines.
The Angel RPG is similar, though it has a bit of a different focus. There are more supernatural options, plus vehicle rules (as they're always driving in Angel), and rules for groups and factions.
Sadly, Eden lost the license before they could finish the line. Fortunately, I was a play-tester, so I got to read the early drafts for these books. Unfortunately (for you) I am still bound by the non-disclosure agreement, something I take very seriously, so I can't divulge how awesome these would've been, though my crack legal staff tells me I can say "very awesome".
Neither of these came out, unlike Ryan Seacrest.
Along with Welcome to Sunnydale (which was a guide to Chattanooga, I believe), and the Investigator's Casebook (which was going to deal with police, crime, and low-key supernatural occurences, like that episode of Angel that had drug-dealing demons), there was going to be an Initiative sourcebook (some fans HATE the Initiative, but soldiers going full auto on vampires always tickled my fancy), a Watcher sourcebook, a monster book for Angel (which would've had even MORE crazy options for supernatural PCs), and a Wolfram & Hart sourcebook, which never even got to the writing stage.
It's a shame the license ran out, by the games hold up pretty well, and allow you to create your own stories, as their are stats for both the actual cast and original characters. You could even rewrite a season that your felt wasn't as good as they others, though none come to mind. *COUGH*Season 6*COUGH*.
The BtVS is simple, fast, imaginative, and fun, and I recommend it highly.