Centauri

A good Event I used to run on my old Arma2 Overpoch server was a "washed up vehicle" event where an Admin would spawn a vehicle on the coast with some loot inside and then announce something like "Washed up Hunter on Chernagorsk coast, first person there gets it".

Another good one I've seen happen is a convoy. The admins declare the route the convoy is following and the players have to seize it and take the vehicles+loot inside.

There are a couple other ones that are self explanatory such as:
-Deathmatch
-Race
-King of the Hill

I hope you guys find this useful as Admin Events can make the game extremely enjoyable for the players.