The game I cut my teeth on (I really shouldn't have been chewing on it), and still my favorite version of the grand old game. An excellent starter for kids and adults alike.
Okay, technically I already own this one, so I'm too cheap to buy another copy.
This is easily one of the most useful books a role-playing gamer can own, regardless of what system they use. It's also an artifact of the halcyon days of the hobby, from just before a weird game enjoyed by bearded men became a money-making phenomenon.