Isn't this what curtains and shutters are for?
Yes, it's what they are for - but they are typically inferior alternatives for the specific goal of preventing light entry.
My parents visited Israel when I was a kid. My grandparents' apartment had Israeli air-raid-quality shutters which ACTUALLY blocked out all the light; they were wooden slats that rolled down and stacked themselves solidly over the outside of the window. You pulled on the cord and the light went out completely - that simple. I expect it helped on noise reduction too, though I wasn't checking then. Ever since, I've taken the lack of this simple, extremely useful feature on any other windows I've ever seen, as proof that the housing industry is dysfunctional.
I have often benefited from recommendations for Things I Didn't Know I Wanted.
Given that Less Wrong is a community of unusually intelligent, critical, and self-improvement-focused people, I suspect we can generate a pretty helpful thread of product recommendations — perhaps even a monthly thread of product recommendations.
Rules: