Who played Serena van der Woodsen in 'Gossip Girl'?

Who played Howard Wolowitz in 'The Big Bang Theory'? Who played Raj Koothrappali in 'The Big Bang Theory'? Who played Blair Waldorf in 'Gossip Girl'? In which TV series is Blair Waldorf a main character? Who played Michael Westen in 'Burn Notice'? Who played Carly Shay in 'iCarly'? Who played Alex Russo in 'Wizards of Waverly Place'? In which TV series is Walter White a main character?