There are two towers attached to the Parliament Building, which is collectively known as St. James Palace - the Clock Tower on one end with Big Ben and the Westminster Chimes. At the other end is the King's Tower, which is the Sovereign's Entry. The King's Tower was renamed Victoria Tower for Queen Victoria's Jubilee, so now they are renaming the Clock Tower to the Elizabeth Tower for her Jubilee.
London Historian's Blog - Victoria Tower has more details.