Warm Window Basic Insulating shade - a *must* for Texas summers (and winters!)
Kume curtains - used thin layers of air to reduce heat loss through windows up to 50%
DIY insulated curtains - Frugal by Choice, Cheap by Necessity
The Warm Windows website has very easy instructions on making curtains with their product Read more: http://www.motherearthnews.com/homesteading-and-livestock/living-off-grid-how-to-make-insulated-shades.aspx#ixzz3P32PyVlc
Grommet Top Insulated Curtain Pair-Trellis Print - at Improvements, surprisingly festive!
Slate grey blackout curtain / insulation curtain custom curtains (all size)
Another temporary option for the colder months of the year is to use curtain clips to hang a thick insulation behind summery curtains.
Insulated curtains - keeps the house warm in the winter and would be great black out blinds in the summer
Aurora Home Floral Lace Overlay Thermal Insulated Blackout Grommet Top Curtain Panel Pair
Frugal by Choice, Cheap by Necessity: DIY insulated curtains