I very excited about the Duchess of Cambridge attending her first state banquet and I hope that we get some good pictures from inside Buckingham Palace. Usually we get good pics of the Queen and only see the rest of the royal family in the background. About which tiara she will wear, I think that either the Halo or Lotus Flower Tiaras would look lovely (with an updo of course).
Another possibility is Queen Mary's Sapphire Bandeau with was last seen on Princess Margaret.