#3 - Sept. 3, 2010, 4:55 a.m.
The others are correct - there isn't really a 'cancel account' specific page, so whether you are simply removing a recurring subscription or you are permanently leaving, you'll go through the same venue.
I do apologize for any confusion this may have caused. =)
I've included the normal steps below for your convenience.
Canceling Your World of Warcraft Subscription: 1) Log in to your Account Management page:
http://us.battle.net/ 2) Select the Game you wish to manage by clicking its box art, then 'Manage Game'
3) This should have brought up your Battle.net account overview. Click on the title you wish to manage a second time.
4) On the right side, there should be a link for canceling your subscription, so long as your account status is set as 'Active' and not 'Pending'