The freakiest one of all are barred owls when they scream.
http://www.stancourtney.com/sounds/birds/Barred%20Owl/2009.05.07_Barred_Owl_01.mp3
They don't always do the hoot along with it. Just the loud rising scream part that will scare the shit out of you at night in the yard. lol We've had one in the woods behind us for years and it still gets me every now and then.