The Next Battleground in WotLK

Nethaera shattered a few people's hopes for a new battleground soon, but reminded everyone about two PvP features coming in Blizzard's second expansion, Wrath of the Lich King.
There are no current plans to release one prior to Wrath of the Lich King. We are focusing on AV improvements for patch 2.3 and also on creating content for Wrath of the Lich King which includes a new battleground and of course the outdoor pvp zone, Lake Wintergrasp.