Github's site is really fast. Many of the pages it displays are dense with information and I think it displays everything well, for example viewing diffs in Github is very good, it smartly wraps all the text so you can view everything on the screen and everything loads fast. Try comparing it to Bitbucket's diff view, which can't wrap text amongst other things. It's light years better in comparison. It looks good at any window width with little wasted whitespace.

Amazon's site works pretty well. Their product range is quite a mess to navigate but I've never been annoyed much by their front end. It seems pretty well engineered, eg. [1]

[1] https://bjk5.com/post/44698559168/breaking-down-amazons-mega...