One player no one is really mentioning is Iverson. He pretty much integrated the street/hip-hop culture into basketball. He is/was an idol for inner city kids and gave the game a new style (whether you like it or not). To me AI has been huge in making the game what it is today
Kevin Garnett is one of the most influencial in this recent era. He transformed what is thought of about what a big man should be able to do. As you see these kids rise from the high school ranks that are all around big men that can play on the perimeter they all say KG is the favorite player who they model their game after.
Most Important in starting something new:
Julius Erving (the slam dunk. I'm nowhere near as educated as the other people, but as far as I know, and it would be great if I was proved wrong, Erving was the first established star of the slam dunk)
Most Important for the NBA:
Michael Jordan (he practically brought the world into the NBA. An easy litmus test: Go to England, the most anti-basketball nation in the world, and ask them this list, Michael Jordan, LeBron James, Kobe Bryant, Wilt Chamberlain. Odds on Jordan is the only one regconisable).
I'm sure that there are other categories (Because I don't believe in ranking things purely by a general definition) but can't think of any at the moment. Moses Malone would be a good one for skipping university into the NBA. You could argue that Jabbar started something new with the skyhook, problem is nobody else can do it.