This is a great question and I'm glad you asked it. First off, don't listen to those who are giving you a hard time about doing the right thing. People who drive without insurance are derelicts who harm society and put hard-workers like ourselves in danger of serious injury and possible death. If they cannot be bothered to pay their bills (or keep a job for that matter), then we can only assume they are not responsible enough to drive a vehicle on our roads.
That being said, the best course of action would be for you to contact your local police station and let them know the license plate and location of the car without insurance. If they are leasing or financing the car, you might also consider contacting their bank to let them know that they are driving without insurance. Banks usually require a low deductible collision and comprehensive plan, and they get very angry if they are not maintained. If you're lucky, they may end up taking the car away from these low-life neighbors of yours. You can figure out any loans they have out if you run a comprehensive background check on these people.
I hope this helps. Keep up the good work.