Okay. I used to say "AH-chee-oh" because it looked Italian but then Jim Dale said "AH-see-oh" so I changed and now Movie!Harry says "AH-kee-oh." I am a fangirl and therefore allowed to have a mini breakdown over such things, shut up.

I too found the accio pronunciation to be the most startling thing in the movie. I always pronounced it AH-see-oh, and I find I'm rather attached to that pronuncation. (Yes, yes. I'd probably find it a little sad, if I didn't care so much.)