All of the above posts make excellent points, and I agree that the fight on any crime (not just gang violence) is never over. As soon as a society deems we've been beat by certain types of crime or criminals, we essentially open the door to chaos.
As far as what can communities do? It is always difficult to tell what will be successful. Certainly, the rebuilding of the family unit would be ideal. Kids who have strong families and strong family support tend not to look for acceptance in innappropriate areas (not as a rule, but generally speaking). I also tend to believe that the people who have the most potential for creating change are the professional sports stars and entertainment icons who most teenagers (esp. the demographics that are most affiliated in gangs) look up to.
I personally have a lot of respect for Eminem's talent and intellect in his industry. I don't necessarily believe he speaks an inherently positive message (and I don't respect him so much on a personal level), but his sense of authenticity and the presentation of his reality is usually both catchy and yet smart. I can't help but imagine what might happen if someone like him decided to really start fighting a war against crime, violence, and insecurity, especially if it was genuine, and truly positive.