The only one which comes to my mind is "Wicked", a fanfic about The Wizard of Oz.
Da Vinci Code has actually very little to do with the Bible. It's more like a fanfic of a fanfic.
Ok, it didn't technically "sell," being a webcomic, but I think that Dan Kim's fancomic "Nana's Everyday Life" was far superior to it's source, the animu "Elfen Lied."
Paramount had an arrangement with some publishers, and maybe still does, to sell "original Star Trek fiction."
I'm told it sells pretty well. Do Star Trek novels count as fanfiction?
What do you define "fan fiction" as? A piece of fiction, based upon a previous work, written by a fan of that previous work?
"Angel of the opera."
50 shades of grey. I win yay