Best digital download sources?

I'm doing a roundup of the best digital download sources (paid or free). I don't mean streaming, I mean where you keep your own copy. What are the best places to download books, music, movies, software, etc? Yes, there's Amazon Kindle and iTunes app store. Where do folks go for Window's software? Or Mac stuff these days? Do folks pay for movie downloads (vs just stream)? And of the black side, what's the best free site?