Roller blinds, cellular shades, Roman shades...

The best product for room darkening and energy efficiency is honeycomb shades, hands down. They come in a ton of different pleat sizes, colors, fabrics, and textures. I would recommend checking out Hunter Douglas Duette Architella Honeycomb Shades. They were rated as being one of the most energy efficient honeycomb shades on the market a few years in a row. They are offered in a wide selection and come with great warranties. You'll have to find a local dealer in your town but most offer free in-home estimates. Here's a link with some good info:

http://www.twoblindguysstl.com/cellular-shades.html

That's right, layered window shades are your your best bet for blocking out the most light. Another bonus of light blocking shades is that they are also blocking out harmful UV rays. An additional thing to think about is energy efficiency. The right window shades can actually lower your energy bills! Check out some of our Halcyon Shades options here for some good ideas on what you might need!