PvPSpec automatically makes sure that you do not enter an arena with the wrong dual spec enabled. It is a lightweight (7 KB) addon that will disable the "Enter Battle" button and cast switching to the spec you designate as your pvp spec.
Usage: "/ps" or "/pvpspec" followed by a 1 or 2 for which spec you wish to use. For example "/ps 2" will set your second spec as your pvp spec.
Feel free to post suggestions/bugs in the comments section.
1.3 Updated TOC
1.2.1 Edited this change log (oops forgot before).
1.2 Added in automatic switching to a PvE spec upon entering an instance. Also reworked the coding to make it much more efficient (even though it hardly took any memory before).
1.1 Replaced ("PLAYER_ENTERING_WORLD") with ("PLAYER_LOGIN") to prevent the "Use /pvpspec" message from being placed in the chat frame every time the character zones.