There's 8 "The Vampire Diaries"-books available in stores right now. + There will be a new TVD-book out in 2012:
1: The Awakening. 2: The Struggle. 3: The Fury. 4: Dark Reunion. 5: The Return: Nightfall. 6: The Return: Shadow Souls. 7: The Return: Midnight. 8: The Hunters: Phantom. 9: The Hunters: Moonsong. (- Will be in stores March 13th 2012.)
Then there's the book series "Stefan's Diaries". - These livres are about Stefan and Damon's past:
1: Origins. 2: Bloodlust. 3: The Craving, 4: The Ripper.