Minutes ago I posted an update to the Better Gmail 2 Firefox extension, which adds all sorts of functionality to Gmail. Since Gmail Labs launched, there's been less of a need for Better Gmail 2 features--so this revision clears out a lot of redundant stuff and pares things down to the items Google doesn't offer (yet?).
My favorite addition to this new version 0.7.3 is the awesome Unread Message Count in Favicon script, which adds that helpful little red unread message count to your Gmail tab's favicon (shown above). Note: A similar script which includes chat alerts is Gmail FavIcon Alerts, which I'll try to get permission to include in future Better Gmail 2 versions.