Every year there’s an excellent aviation fair at Rotterdam Airport in the Netherlands. You may know it as Luchtvaartbeurs.
I attended a few years ago and enjoyed the mix of aviation collectibles and stalls with and active airport. That year they organised airside tours and a drive down the runway in a bus.
This year they may be offering the same, but the highlight has to be the sightseeing flights by the Dutch Dakota Association DC-3.
The fair runs from 10am-4pm on 16 April 2011 inside the terminal at Rotterdam Airport. Entrance is free. More details here: http://www.scramble.nl/dsc.htm