We got the cheapo vinyl roller blinds from the hardware store for the nursery because we really wanted to block the light. it works great, and dissappears when they are open, and you can keep your cutesy curtains!
DIY No-Sew Fabric Covered Blackout Roller Blinds by The DIY Mommy. Just use spray adhesive, fabric and ribbon for an exciting update to your roller blinds! *Footnote: An idea for craft room and a great project for 'the beginner'.