I loved all the stories on this fic rec list: http://myutopia.livejournal.com/54324.html

Some are R-rated, but include a warning for that. I'd start with Parabiosis - amazing story. And Fathoms Five is also amazing (it's a futurefic, though). In fact, all the stories by that author (Penumbra).

Actually, Labby, have you seen the second movie, I Want To Believe? If not, you must! I loved it.

Julie smile

Mulder: Imagine if you could come back and take out five people who had caused you to suffer. Who would they be?
Scully: I only get five?
Mulder: I remembered your birthday this year, didn't I, Scully?

(The X-Files)