In my family, we've always just called the grandparents grandma & grandpa. To tell them apart, we'll call my mom, for instance Grandma Linda. I was kidding with my kids that since my parents live in the south, that when my parents visited us last month, we should call them meemaw and pawpaw. The kids thought that was hysterical and called them that the whole trip. My parents, who actually hear people called that all the time, didn't get why my kids thought that was so funny.
I had a friend whose family called the grandfather "pop pop" which I always loved.
So, what do you call the grandparents in your family?