What's the wildest anime/non-anime crossover anybody's ever come 
up with?  (Note:  Power Rangers, and similar shows, do NOT count as 
non-anime.

The champion has to be <your anime here> + Star Trek.  So incompatible that
you sometimes have to time travel _and_ dimension travel just to get the
crossover.

In a way, it even beats out Ranma 1/2 + 60 Minutes, as well as Ranma 1/2 +
Predator (which at least takes place in the same time period).

For sheer numbers of crossovers, Undocumented Features.