Who played Blair Waldorf in 'Gossip Girl'?

Who played Penny in 'The Big Bang Theory'? In which TV series is Penny a main character? Who played Howard Wolowitz in 'The Big Bang Theory'? Who played Raj Koothrappali in 'The Big Bang Theory'? In which TV series is Blair Waldorf a main character? Who played Serena van der Woodsen in 'Gossip Girl'? Who played Michael Westen in 'Burn Notice'? Who played Carly Shay in 'iCarly'?