I used to have Discovery Wings, and I wasn't all that impressed. It mainly shows military orientated stuff, especially WWII material.
Flight Deck is indeed interesting, although it is dated. One episode is about a flight on an Air UK Leisure 737-400, this airline stopped flying quite some time ago.
The best thing I ever saw on the channel was a series about the B777, called 21st Century Jet. This covered the entire development of the 777, from initial production to service entry with United. It really was an excellent series, and I'd love to see it again.