They look pretty lightweight, so make a satelite that will reflect sunlight down onto your house at night, reducing your electricity needs for lights. Just kidding
Since there are so many, you can use them for a few projects. One idea is to lay them at a certain angle in front of your south wall, reflecting more light into the house during the winter. During the summer they can be used to shade the windows as NiHaoMike suggested, or even the roof. I've also been thinking about a vertical wall of mirrors for the east/west windows: During the winter you put mirrors on the north side of the east/west windows so that they reflect more light into the house. In the summer, they get moved to the south end of the window frame, with the reflective side facing north. This shades the window from direct sunlight, but reflects light from the north into the room.
This "wall of mirrors" could be hinged to act as a closeable storm window, so that it doesn't stick 2ft. out into the wind.