This mod by Shambarimen keeps track of all of your battlegrounds.
BGTracker keeps track of all of your battlegrounds. It tracks your wins, losses, and average honor per game. It tracks all existing battlegrounds (Alterac Valley, Arathi Basin, Eye of the Storm, and Warsong Gulch) and it's very lightweight, using virtually no resources. There's no configuration; just unzip it, drop it into your AddOns folder, and you're ready to go.
In order to see your battleground statistics, open your character panel and select the "Battleground" tab in either the right or the left statistics window. Mouse over the battleground you're interested in, and the tooltip will tell you about that particular battleground.
BGTracker was inspired by Titan BattleTracker. It is an Ace3 mod.
BGTracker doesn't know anything about arena matches.