Buy a whole bunch of frames. Buy more than you need, you can always take some back. Buy a variety of frames, but mostly 4x6 and 5x7. Get a few 8x10s also. Try to stay away from more than two of the same frame in the same size, but whatever. It might also look good with all frames EXACTLY the same. I grabbed a couple composite frames as well- three or four photos matted and mounted in the same frame, but chose not to use them. It might work well in your setting, esp. if there is a common theme in a few pictures.