Alot of people love the PVP in minecraft, and a good arena is something this server doesn't have.  You have a few mini-games now but many of them can only be played during server events.  What if a few people want to duel it out?  They can make bets against each other and it would be a fair fight, not who has the best enchanted armor.  Anyway here is something I built yesterday that I thought would be good to kick start this idea.

It is a four player archery battle with platforms to jump across for a close quarters battle.  But it comes at no risk.  Miss a jump or get hit by an arrow while jumping across mean certain death with lava lurking in the depths.

And here is the schematic link.
http://www.planetminecraft.com/project/archery-wars/











And you can't really tell in the pics, but the lava is about 10 blocks below the structures so nothing will catch on fire randomly.