good ideas so far. when i was back at the prowlers server, we had a very unique event organized. it would require some scripting but i can probably ensure to be entertaining. we had a portal from the capitals that led to the empty region of hyjal. it was here that we fought an army of vicious bloodthirsty.... BUNNIES!!! yes i know it sounds weird but it was very well organized and provided some awesome gear as well.
it all started when pommy was complaining about the server being too quite and he wanted some kind of huge army of something to take down. that's when he suggested an army of bunnies. had the normal bunnies set up on stormwind's bridge but it wasn't enough. so we eventually got some gm's to work on scripting the bunnies and placing them in hyjal.
it proved to be entertaining and was open to all levels, with the portal leading to a level 10-area. you could then walk farther to the stronger territories. all the way up to three bosses, Duke, Queen and King Bunny! it proved to be the hardest thing i've done and was fun to think about being torn to shreds by an army of malicious bunnies.