The black out cellulars I bought several years ago work well, but light seeps in from the sides. There is a newer version of black out cellulars that has rails on the sides. I don't have a link at the moment, but will look.

Edited to add links:
Slumbershade
https://www.youtube.com/watch?v=skAHFPOeR_M

Here is a link that might be useful: Comfortracks cellular

This post was edited by graywings on Wed, Apr 30, 14 at 12:39

blackout cellulars work really well. You can also put a film on the outside of the window that reflects the sunlight or blocks it altogether.

Had blackout cellular blinds in a previous house. They blocked light in our east facing bedroom well. Some light seeped through the edge as expected. They block a lot more light than the non blackout. The two issues I had with them are they're functional but not decorative and it's almost all or nothing with the light. The blinds are open and let in light or closed and block most of it. In my office it wasn't easy to block the glare but keep some light.

I installed NDB 3/8" single cell blackout shades in my bedroom that gets full afternoon sun to try to keep the room cooler. They really helped reduce the heat in the room. There is some light seepage on the sides, but it doesn't bother me.

I am very sensitive to light and those cellulars with the tracks look great. Right now I have just the standard blackout shades. Over those I have blinds so I can filter light, and on top of that I have blackout drapes. Amazingly enough, it still doesn't block all the light and I am still looking for the solution.