I heard about this tool from Michael Hyatt. It's pretty cool, its called Similarweb.com
I could write a giant blog post about it, but in the end it would take last time to just go use it. You learn all sort of great insights into your website (that in theory you can get from analytics), but you can't get analytics about your competition – and you can enter their URL and find out all sorts of cool stuff about them. You can see if what people are paying on their site, where there traffic is coming from. You can see how their traffic got there and much, much more…
It also shows you the top websites (which you can choose different categories).