I know stamps aren't that collectible anymore, and this is hardly an uncommon one, but it's a beauty:

A first day cover celebrating the Apollo 11 and the "First Man on the Moon"
The stamp is Scott C76
10¢ postage
Postmarked twice: July 20, 1969 (the actual day of the moon landing) and September 9, 1969 (presumably when the stamp was issued.
The cachet was designed by Fleetwood

I believe this is the very first U.S. stamp to picture a living person: you don't see his face, but the astronaut who was the first man on the moon was, of course, Neil Armstrong.

I was 10 years old when this happened, and it tickled me no end.

Excellent condition.