If you're looking for some more RvR action outside of Warhammer Online, then you might want to take a look at Gala-Net's newest addition to their MMO lineup, Aika.Aika is a new free-to-play MMO with the same type of nation versus nation bent that Warhammer and World of Warcraft provide to their players. Players get to defend territory during castle sieges, can steal artifacts from the enemy side, a la Dark Age of Camelot, and participate in the standard PvP battlegrounds.
The game has just gone into a closed beta testing phase for America, but getting in couldn't be simpler. Simply go visit the Aika website, fill out a survey and you'll be entered for a chance to participate in the closed beta.