What kind of a microscope would be good for a 9 year old boy who is very smart and very interested in science?

I have a 9 year old grandson, who is very intelligent and loves anything to do with science. He has "hinted" about wanting a microscope for Christmas, and myself being very "unscientific" know nothing about these things, but I would love to get one for him. So, where do I go for guidance, and of course some kind of help in what to get?