If you are using a new build of Chromium 13, you can now go to “about:flags” and enable “Compact Navigation”. After restarting, you can right click any tab and select “Hide the Toolbar”. If you also hide the bookmarks bar, you can make Chromium take up only as much space as the title bar.

So far this is only available in the Windows builds, but it should be coming to Linux and OS X soon.