The World of Warcraft Armory is a searchable database of all characters, guilds and arena teams in World of Warcraft. Blizzard’s plan is to have the data be real time at some point, though for now it appears to be updated somewhat irregularly (appears to be updated every couple days).
So, for example, I can show anyone the character sheet for my main character, Dennett. Notice the 3,899 PVP kills — almost all of those are from world PVP as I find the Battlegrounds rather dull.