I found QTTabBar from this post, and rather like it. One thing though, if all you're looking for is tabs, disable the ButtonBar and other toolbars (in the View > Toolbars menu) and dig through the settings to disable some of the unnecessary ones. I suggest unlocking the toolbars and moving the tabbar to the
right of the menu bar; that way it's always visible and not taking up another whole row, but still accessible.
Also, check out
Quizo's version of QTTabBar (same name) at
http://qttabbar.wikidot.com/. Quizo was the original creator, but has currently stopped developing his version of QTTabBar and
ShiningMasamune's version is now the main one. But the versions are slightly different (Quizo's is a bit more refined and offers a few more options, but ShiningMasamune will be releasing a new version that is two years in the making and promises quite a bit more). Read the blog at
http://qttabbar.sourceforge.net/ for more information.