I was introduced to fan fiction by my older sister 3 or so years ago. Since then, I have been reading fan fiction on a regular basis. My favorites include:

Harry Potter: Ron/Hermione, Draco/Ginny, Neville/Luna, occasionally Harry/Ginny

Bones: Booth/Brennan, Hodgins/Angela, Daisy/Sweets

Buffy the Vampire Slayer: Buffy/Angel, Buffy/Spike

Angel: Angel/Cordy, Wes/Fred

Vampire Diaries: Bonnie/Jeremy, Elena/Damon, Alaric/Jenna, Caroline/Tyler

Hunger Games: Peeta/Katniss

I have read some fan fiction of different books/movies but they weren't my favorites.