Wouldn't you know it, just after I finished painting my apartment, I discover insulating paint. A NASA research partner in Florida called Hy-Tech has developed a series of insulating paints that are now on the market. It is interesting to note that the paint also insulates sound, so when you use it, you get a much quieter home, apartment, or business.
Their web site claims that you get on average a 35% reduction in heat transfer. This means that it will keep the heat in during the winter, and the cool air in the summer.
They have lots of impressive testimonials on their site, be sure to check them out.
The paint cost around $38/gallon, but you can also get an additative to mix into your existing paint.