My most prized Playbill is one from "Hold on to Your Hats" autographed by Al Jolson.
Others:
2002 The Crucible signed by Liam Neeson and Laura Linney
1998 Parade signed by the entire OBC
2000 The Wild Party signed by the entire OBC and Michael John LaChiusa
2004 The Frogs signed by Nathan Lane and Roger Bart
I also have several Playbills from the '40's like Oklahoma, High Button Shoes, and Carousel.
"You pile up enough tomorrows, and you'll find you are left with nothing but a lot of empty yesterdays. I don't know about you, but I'd like to make today worth remembering." --Harold Hill from The Music Man