From iPhone Development Wiki

SBDisplayStack was a private class in SpringBoard that arranged SBDisplays until iOS 6. There were 4 display stacks, all being private and inaccessible directly, due to stripping. In iOS 6, the class was removed and replaced with SBWorkspaces for managing displays. As of 3.1, these 4 stacks were:

VM address (3.1, armv6) Stack name
*0x107540 __SBWPreactivateDisplayStack
*0x107544 __SBWActiveDisplayStack
*0x10753C __SBWSuspendingDisplayStack
*0x107548 __SBWSuspendedEventOnlyDisplayStack

If you want to use these stacks without hardcoding the pointer, you may hook -[SBDisplayStack init] and store a reference of the return values.