One of the coolest (and rarest!) types of Wing Commander memorabilia is dev team shirts. Origin used to hand out special shirts to everyone who worked on a particular game... so only a few examples of each ever existed. They often feature interesting new art, and can even sometimes add a little bit of information to the Wing Commander canon (like this one, which created a squadron designation).
Here's one that really takes the cake, though -- the dev team shirt for the original Privateer, featuring a very cool blueprint of the Centurion heavy fighter! This artwork doesn't appear anywhere else... which is a real shame, because it's very cool. There are high resolution images linked below -- anyone want to take a shot at figuring out the specifications?