I just did an 'airplane' party for my 7 year old.  We visited a near by airport (small - mostly gliders) and were able to see tons of older planes in the museum.   The kids got free pins and bumper stickers from the manager.   They loved being able to touch a real plane and to be able to sit inside one.    At home, instead of pin the tale on the donkey, we did pin the pilot on the plane.  I drew an airplane on posterboard and cut out stick pilots for the boys to place in the cockpit.   For decorations, we made many, many paper airplanes and hung them from the ceiling.  We also used a 'red white and blue' theme with plates, cups and balloons and crepe paper.   The party bags were filled with 'teenie beanies' and then all sorts of aviation trinkets.   The cake was a run-way sheet cake with a big US Air 747 on the runway.   It was a fun and different day and was not very expensive at all.