I was getting a key made today and found the nicest mementos for pets. They were at the Engraving kiosk in Burlington Mall, and the cost is only $10 plus engraving (80 or 90 cents a letter), and you may not even want to engrave it.
They were actually quite nice and not too big (maybe 5 inches?); the picture doesn’t do the left one justice (it looks like a fake moon rock in the photo!) For those of you who might want to have a small remembrance, I think this might be a good choice.