Tor Norbye shows nice screenshots of local editing file history (with version diffing), and the brand new diff view. Note that the file itself is not under version control – diffs are against auto-saved version.
See: Tor Norbye: “Ruby Screenshot of the Week #6”. The smooth curves are very cool.
See also: Meld: open-source visual diff and merge tree for Gnome. Supports CVS, Subversion, Bazaar-ng and Mercurial.