this was on wikipedia's coldplay page:
There have been distinct rumours of a new album in the works and thus are disclosed as true, the album is a B sides compilation album, the album Castles (2006) is finished and remains unreleased worldwide. An official release date is not yet set, but it is hoped to be released December 2006. Some are sceptical toward the legitimacy of this album and there has been some notable media leaks as stated on various web forums. The Album contains some 15 tracks, four of which are live recordings.