Vampires

Vampires, the undead — fantasy? science fiction? horror?
Because vampires often have some associations with magic and magical beings (being supernatural), vampire stories are often defined as fantasy.

Cirque du Freak (series) — Darren Shan
Dangerous Girls — R.L. Stine
Darkangel — Meredith Ann Pierce
Demon in My View — Amelia Atwater-Rhodes
Icemark Chronicles — Stuart Hill
Look for Me by Moonlight — Mary Downing Hahn
New Moon — Stephenie Meyer
Silver Kiss — Annette Curtis Klause
Sunshine — Robin McKinley
Thirsty — M.T. Anderson
Twilight — Stephenie Meyer

And of course, Buffy & Angel, in paperback & graphic novel format.

For a nearly comprehensive encyclopedia on vampires, see Omnigraphics The Vampire Book: the Encyclopedia of the Undead.