Ask HN: Which sites in your opinion have great design/UI/UX?

I know this is a subjective question but interested in HN view. I m more of a back end hacker. I do have a lot of interest in front end design including UI/UX but wanted to get your opinions on some of the good ones to look at. For example, I personally use freshbooks.com for my consulting and love their design/UI/UX. Also, my second criteria is that these sites work ok with older browsers upto IE7. Freshbooks again does this well.