Last time I mentioned the methods I used to resolve my Mac freeze issue. And I found the method to run the Force Quit by this shortcut key: Cmd + Option + Esc. However, if the root of cause is the background task then you might not able to resolve it.
So better you set another shortcut key for Activity Monitor to open, like that you are able to quit those hidden task.
PS: Here also needing useful method to interrupt the BeachBall. http://superuser.com/questions/106483/interrupting-the-spinning-wheel-of-death