How many times have you had to throw away over-ripe bananas because you didn't have to time to make some with them? I love bananas and hate letting them go to waste, but many times that's just what happens. What I have found is that you can freeze them in a plastic zipper bag to use later. In order to do this, put them into the bag and squeeze out as much of the air as possible and seal. When you have time to bake, let them thaw and use.
I've never let them stay frozen too long, as I'm not sure how long they stay good in the freezer. If anyone knows, please post it in the comments of this article.