It's called the golden rectangle which has a ratio of 1:1.618 according to wikipedia http://en.wikipedia.org/wiki/Golden_rectangle. 35 mm is close at 1:1.5
I don't know that it has much to do with our natural field of view though, but we do find it pleasing for some reason. It's also present in a lot of natural proportions, which may be the reason we like it.