Wow! The Dixie Chicks seem to be on a flight that never ends. The hip country trio's debut Monument album, Wide Open Spaces, has now been certified quadruple platinum -- selling more than 4 million copies. The album was certified by the RIAA recently along with other certified albums such as Faith Hill's Faith (2 million)and Alan Jackson's Who I Am (4 million), plus both Clay Walker's Greatest Hits and Toby Keith's Greatest Hits, Vol. 1 going gold -- selling in excess of 500,000 units.