TabBinder will automatically change your tab key binding to only target enemy players when in PvP zones, and to target all enemies when not.
Despite it being named "TabBinder" it will also work for keys other than just tab. First it will check to see if you currently have "target nearest enemy player" bound, if not then it will check for "target nearest enemy" (the default tab behavior). If you have either of those already set then it will use your current key binding to alternate between the two different functionalities, if not then it will resort to tab.
No configuration needed so there is no options menu, just install it and you're good to go. It will switch to "players only" when in arenas, battlegrounds, and Wintergrasp. Great for those of us that like to PvE and PvP... no more tabbing through totems after forgetting to set it, or wondering why you can't change targets in a raid. :)