Title: Gilead
Author: Yahtzee
Pairing: Mulder/Scully
Spoilers: the show's over--does it matter anymore? ;-)
Summary: Two people find each other again in a broken world, but can they save each other too?
Link: Gilead
Why: Because while I would never have thought of this crossover, it works so well it's scary and the result is one of the best apocalyptic XF fics ever not to include aliens. *g*

Title: The Magician
Author: Suzanne Bickerstaffe and Jennifer Lyon
Pairing: Mulder/Scully
Summary: Investigating the appearance of a "gargoyle" at a DC lab sends Mulder and Scully on an interdimensional odyssey, to a realm they are fated to save, a realm that is fated to change them forever.
Link: The Magician
Why: You know that epic I've been working on forever? The fantasy AU Stargate one? This is, ultimately, the root cause of it, and its magic hasn't faded since I stopped being a M/S 'Shipper, which should tell you something. *g*

Title: Umbra
Author: Dawson E. Rambo
Pairing: Mulder/Scully
Summary: Just how far would you go to save the world?
Link: Umbra
Why: This is one of the classics of the fandom, and with good reason: a nail-biting, stunningly plotted thriller more complex and gripping than many published novels. It's just a pity the author never did finish the sequel. :-/

Title: The Last Worthless Evening
Author: Anne Hedonia
Pairing: Doggett/Scully, Mulder/Scully implied
Summary: "A necessary emotional arrangement."
Link: The Last Worthless Evening
Why: Considered by many (me included) to be the definitive DSR fic, and one that doesn't ignore Mulder's place in the equation.