These are just some ideas that I've kicking around in my head.

Inuyasha/X-Men (movieverse) crossover. I saw so many of these on fanfic.net as badfics, I wondered if I could do one believably.

Stargate/X-Files crossover. Mulder's sick, but there is a way to cure him...

Harry Potter smut set to the tune of Love in an Elevator.