Pop superstar Britney Spears put on a pair of surprise performances over the weekend during which she unveiled several tracks from her new album, "Femme Fatale," which is scheduled to be in stores March 29th.  Spears performed a ticketed event and a later free show at the Palm's Rain Nightclub in Las Vegas. In addition to the album's first two single, "Hold It Against Me" and "Till the World Ends", Spears debuted "Big Fat Bass" from the album, which was produced by the Black Eyed Peas' Will.i.am.