The original and best - Emma Jeffs Otto Adhesive Window Film.
Then I was in Lincraft one day and found some plastic table runners that I thought would do the job nicely! For a couple of bucks a metre, I simply cut it to fit, then stuck it on the window with one of those spay-on adhesives. (I haven't taken it off yet, so not sure how ruined the actual glass is by the adhesive!?) Considering I got change from $5, I think it looks a bit of alright!