The following list is from Cancerman's Lungs web site, and as far as I know was authored by the site's owner, Mark Anthony Gray:
The Top Ten X-Files crossovers we'd most like to see ...or not:
10. Twin Peaks -- The only time Mulder would actually get spooked.9. Anything with Jim Carrey.
8. Star Trek: Voyager -- Anything for Scully in a Trek uniform.
7. Seinfeld -- Mulder and Jerry Seinfeld talk about nothing while Kramer puts the moves on Scully.
6. Dark Skies -- Mulder and Scully mistake Eric Close for Ratboy.
5. Friends -- Mulder and Scully discussing relationships over enlarged cups of coffee.
4. Star Trek: Deep Space Nine -- Scully would make the perfect Bajoran.
3. Dark Skies, Part 2 -- The counterpart faceoff.
2. Any Aaron Spelling production -- Mulder and Scully try to figure out why the show is so popular, and get frustrated by the airheads and soapy plotlines.
1. A soap opera -- Mulder discovers his long lost biological mother, and his twin brother tries to kill him while Scully dies, returns from the dead, and gets in a love triangle....