I've had a few get thrown up to me at Shea, like Armando Benitez, Steve Traschel and Jaime Cerda. My little sister, who was 8 at the time got a ball from Luis Castillo and we got him to sign it. Matt Morris signed a ball as well (one he threw up to me). Fernando Vina (when he was good), Roger Cedeno, Vance Wilson and Sean Green (my dad at first thought he was Gagne lol) are a few others that I've gotten autographs from at a game.
I also asked Darryl Kile for a ball when I was at Shea. He promised me I'd get one since I was the only one there (or at least who saw him) and it was in the rain In fact, he said "count on it." He never gave me the ball....he passed away soon after.
My dad actually got one when he was growing up. It was Seaver vs Gibson. Gibson was hitting and he fouled one into the stands. It hit my dad's mom in the stomach and my dad recovered it on the ground. She wasn't seriously hurt, but Seaver vs Gibson is pretty sweet (its whereabouts remain lol).