I do this all the time. Slice the bananas about 1 cm (3/8") thick. Place the slices in a zipper food storage bag, being sure to squeeze all the excess air out of the bag. I put one banana per bag. Toss the bags in the freezer. They will retain their color and most of their flavor for a couple months. Eat them frozen or very soon after they thaw. I experimented with the lemon juice thing, but I found the easiest method to keep the bananas from turning brown was simply to make sure there wasn't any extra air in the bags before they went into the freezer. If you want to save bananas for recipes like muffins and breads, just freeze the entire banana in a sealed bag. When ready to use, thaw the banana, remove the peel and use in your recipe.