I recently posted my take on the Buffy characters in d20 Modern terms and thought I'd share it here.
This is my take on the iconic characters from Buffy Season 3.
Buffy: Occupation (Adventurer), Fast 4/Martial Artist 2/Slayer 8
Giles: Occupation (Academic), Smart 5/Occultist 7
Willow: Occupation (Student), Smart 3/Mage 7
Xander (Xander's the only real toughie- this take on him is based on the fact that he just seems to take a boatload of punishment and just keep coming): Occupation (Blue Collar), Tough 7/Soldier 3
Wesley Wyndam Pierce (Academic), Smart 5/Occultist 4
Faith (Criminal), Strong 3/Martial Artist 3/Slayer 8
(For the record, were I actually doing such a campaign, Id make a Watcher class and a new Slayer class- but the existing classes I picked emulate their abilities to the degree that I know I'm not the ONLY watching Buffy).