Hmm. I could go the stationary route. I have some somewhat nice small format stationary, though it's blue and not as professional looking as the cards....
I also did think about addressing it to one person and conveying thanks to all of them in it....
Hey, what about addressing it to the "hiring committee" or the "hiring panel"? I could then, inside, write something like "Dear Mr x, Ms. y, Mrs. J and Mr. L" or something like that.... Damn, damn, damn - why did I have to run out of cards???!!!