From time to time guilds or groups of guilds organize player organized events open to server-wide participation (level of participation varies depending on faction who sponsors event and type of event).
- Running of the Bulls
- Blood of Vengeance (on Norgannon) recently sponsored an event they called "Running of the Bulls" inspired by "Gnome Football" listed below.
- Hellfire Rematch
- Necrosis and Just Got Banned (on Shadow Council) recently sponsored an event they called "Hellfire Rematch" (presumably based on a previous event called "Hellfire Match").
- Unnamed event
- Clouded Minds (on Silvermoon) sponsored an unnamed event in late August 2007 similar to "Gnome Football".
- Gnome Football
- Eternal Keggers (now on Norgannon) supposedly hosted a "Gnome Football" event on Terenas in 2005 or 2006 - Teams of 4 Alliance players attempted to run a level 1 naked gnome "football" from someplace starting in Eastern Kingdoms (like Dun Morogh) to some location in Kalimdor (probably Silithus or something equally silly). All players were flagged at all times. Horde was encouraged to "make things interesting".
Druid Raid Event
- Druid Raid Officers  (on Boulderfist Europe), and a guild not yet known on the server Kel'Thuzad US, Biannually hold a Druid Event around Jan. 11th. They encourage all druids to join in on the event, as long as you are a Night Elf, and since their guild is all druids, they host it. Druid guilds on other servers are trying to get in events like this. The DRO go from Moonglade, fly to Astranaar, run to The Crossroads, raid it, then make their way straight into Orgrimmar. Plus if the thought hasn't crossed your mind yet, if you have an all class guild, you could do something like this. Check out the event here: . Also check out Druid Event 07x here: 
Listing a server events on WoWWiki