Well there is a bunch of stuff to suggest but one thing that popped in my head the other day was like a village on village challenge type situation. For instance you'll have like sand and sound fighting and all that but you just wanna duke it out in one nice battle for bragging rights to see who really is the best.
Event:Ninja War
Two villages fight it out to see who is the last standing.
Rules and guidelines:
Each village and their participants are on the opposite side of the of a battlefield, meet in the middle, self explanitory.
Genin and up of course.
Limited Aoe's maybe thats your decision.
Goal:
Be the last village standing.
Or
Murder Enemy Kage.
Reward:
Exp and free GA maybe?
It may seem far-fetched but its just an idea.