The Camelot Herald: Guild Database - Search for characters and/or Guilds on a particular server, or browse the list of Guilds. - http://guilds.camelotherald.com/guilds/
Crusaders of the Mist - Guild that plays in all three realms. Albion: Lancelot. Hibernia: Morgan Le Fey. Midgard: Palomides. - http://www.crusadersofmist.org/
Dalharen - A guild spanning all three realms. Albion on Kay server, Hibernia on Galahad server, and Midgard on Bedevere. - http://www.dalharen.com/