The Xfce 4 Panel supports multiple panels, with many options for their position, appearance, transparency and behavior. There are many items available by default to full fit a panel, like application launchers with detachable menus, a graphical pager, a tasklist, a clock, a system tray, a show/hide desktop switcher, and even more. It offers an easy way to add items using a dialog, and to move items accross different panels. It's compatible with the numerous panel plugins available from the Xfce Goodies Project page.
Panel plugins from the Goodies Project page
svn co http://svn.xfce.org/svn/xfce/xfce4-panel/trunk xfce4-panel