I was at the Rock N' Roll Hall of Fame this weekend, and this was the only Beastie artifact I came across: Mike D's goggles and dish gloves from the "Intergalactic" video.  (It looks like Mike's gloves suffered some collateral damage from the robot/giant-space-squid fight.)

I also came across this: Chuck D's original sketch for Public Enemy's logo. Part of me thinks it would be cooler if it was just sitting in a junk drawer somewhere in Long Island.