I like to use naniwa's 2 gate robo expand / immortal bust. it hits at 8 minutes with 2 immortals and some gateway units while securing an early expand. very strong, and it leaves you pretty well set up for an economic mid game. It's pretty crippling if you can force a lift of the natural CC and the immortals pretty well demolish bunkers if you FF away scv repairs. If the defenses are too strong to bust through (with a CC first that's almost never) you can still drop 4 more gates, a forge and whatever tech right behind it and be in good shape for a macro game.