"The Craziest Person I've Met This Week" - Fight Club/Potter crossover, NSFW, Remus/Narrator. (With a pairing like that, would you expect it to be work-safe?)

"In Plain Sight" - Potter, Lucius/Luna Lovegood. NSFW.

Edit: bonus silly via ataniell93: "Ships in Sixty Seconds! A Parody of Fangirlish Proportions!" Hermione/Snape, Harry/Draco, Marauder!Sirius/Marauder!Remus, Ginny/Draco. Silly, not entirely safe.