You know I think I was the one who origionally posted 4 and 5, I sure 
haven't seen them in a while.  Here's a few newer ideas.
1 Movie night:  Ok this is a steal from antartic Jam where the main characters 
from four of the books got together each one bringing one video which everyone 
watched.  So what would Ranma Saotome, Kasuga Kyosuke, Usagi, and Nuku-Nuku 
enjoy watching and how would the other's react to it(Or subsititute any other 
characters.)
2 Actually I may have mentioned this before but: A crossover between Devil 
Hunter Yohko and Buffy the Vampire Slayer.  With the master dead and the 
Hellmouth closed, the town is in a state of calm as it were.  So naturally this 
is when Buffy is given the chance to recieve a simester abroad in Japan.  And of 
course it's also at this time that an ancient vampire has come to town seeking 
the blood of the Devil hunter.  My own take on a good Opponent is the only 
Slayer to become a vampire.  There haven't been any other's because it's well 
known that she became a total uncontrollable lunatic afterward.  Thing is she's 
hooked up with a deamon who's partially stabalised her mind.  She still swings 
from mood to mood, but the varying forms of psychosis have ended.
3 A Ranma Gold Digger xover.  Dr. Peachbody had decided that Ranma and Akane's 
decendants will be threats to his the future he's creating so he plans to have 
Ranma executed then brainwash Akane to fall for Gosenkugi.  The latest Gold 
digger suggests that Benji's Genetic augmentation coupled with his training in 
"Doggie" Style Martial arts might make him dangerous enough to take out Ranma 
and the rest.  However I think that the Nekoken would make a really great foil. 
 And this would be the first time an opponent of the Nekoken wasn't A, wiped out 
in the first three seconds, or B, gave up as soon as they saw what they were up 
agains.