Update (2021): Better than the suggestions below is to use LED inserts that fit into the recessed lighting and block air from escaping.
The way to stop all that hot air from escaping through the ceiling is to build boxes around the light fixtures, up in the attic. I've heard from an insulation contractor that the boxes can be made of cut pieces of drywall or styrofoam, and should be no closer than several inches from the light fixture, since the lights can produce a lot of heat. Another approach is to replace the fixtures with the kind that don't leak and can have insulation pushed right up against them. These are quite inexpensive, but they require fiddling with wires during installation. More info can be found elsewhere on the web about this.