These are repos for various Mercurial development:
http://selenic.com/repo/hg - the main repository
http://hg.intevation.org/mercurial/tah - Thomas Arendsen Hein's outgoing changes
http://hg.serpentine.com/mercurial/hg - Bryan O'Sullivan's outgoing changes
http://www.serpentine.com/~cmason - Chris Mason's Mercurial Queues extension