Free hosting of Mercurial repositories
Here are some places that provide free Mercurial hosting:
Alioth (Debian's GForge instance) supports Mercurial and the repositories are accessible via hgweb.
ShareSource.org - A Sourceforge-like server for hosting projects. Supports Mercurial out of the box
MercurialOnSourceforge explains how to host your repositories on sourceforge.
Intuxication: free Mercurial hosting (in French).
freeHg - simple postmodern developer-centric hosting
SSHControl.com - Free hosting for Mercurial, Git, and Subversion over SSH. Also two paid levels at $4.75/mo and $9.75/mo.
It is planned to offer free hosting on hgserve.org.
Also see ServerInstall and PublishingRepositories if you want to host your own repositories.