Before we get into the minutia of what what makes some GMs better than others, let's acknowledge the obvious: Championships are almost always won on the backs of hall-of-fame players who are selected high in the draft.
Kevin Durant, Kobe Bryant, LeBron James, Dwight Howard, Derrick Rose, Chris Paul. You either have that guy or you don't. And if you don't, there's no amount of cap wizardry or advanced scouting that will push your team into contender status.
Of course, this isn't the NBA of 10 or even five years ago.
Back then, acquiring a franchise player via trade or free agency was a near impossibility; elite players in their primes weren't available, and a team's best bet was to strike it rich in the draft. But now that the game's stars have begun forcing their way to the destinations of their choosing—a problem (if you think of it as such) feebly addressed by the current CBA—GMs have added the basketball executive equivalent of the home run ball to their toolkit.
And so the following list is an amalgamation of executives who "went yard" with big-time acquisitions, as well as others who have found prosperity in the League through tried and true means.