Whatever they are - they are pretty!
I think they are hydrangea- or atleast they look very much like hydrangea. There are a ton of differen't hydrangea varieties so maybe it's just a variety you're not used to. :)
It looks like a snowball bush.
My mom called this a snowball bush and the leaves are identical to my hydrangea. The type of soil determines the color. A little lime would probably turn it pink or blue next year.
Ah yes! Snowball bush is what it is. And it is appropriately named. They do look like fluffy snowballs! Thanks ladies!