BitBucket
I recently read this article comparing BitBucket and GitHub and did mention in in a previous post on Git. Apart from well defined differences like BitBucket is a social repository for Mercurial writting in Python whereas GitHub is obviously for Git written in Ruby with bits written in Erlang.
So, I decided to try BitBucket out and I must say although the UI is quite similar to GitHub but it is still not as intuitive and can be improved massively in terms of overall navigation and organisation. But, hold your thoughts, if you are going to write Mercurial off on the basis of BitBucket then atleast check this article out by Geoffrey Grosenbach before you do so.