These are the "boxing servers", or places where there are a lot of boxers.

EU - Alliance - Outland - Autobots Roll Out
EU - Horde - Grim'Batol - GIMP

US - Alliance - Kil'jaeden - Legion of Boom
US - Horde - Blackrock - But Mom I'm Multiboxing
US - Horde - Magtheridon - The Zerg