This site has some very useful information. If you take action now, you could nip this yourself before someone gets seriously hurt.

http://www.mysmartpuppy.com/ask-us/articles.html

There are several articles on this page. Read these under Problems and Solutions.

Agression Basics
Nose Nudging
Question Dog Slams Into Me
Signs Trouble is Brewing
You're Grounded!

If you haven't done an actual obedience class, you should get signed up for one. Also, how much exercise does he get? How much mental stimulation does he get? Most dogs need a job or they create one for themselves. He sounds like he needs exercise and lots of it. A job can be anything it doesn't have to be agility, herding, guardwork. It can be, several sits while you are cleaning your home/room. It could be obedience games while fixing super. It can be playing fetch in the back yard. It can be hiding treats in the living room. As long as it is something that stimulates the mind. Just as people need to work everyday, so do most dogs. EVERYDAY.

As one of the trainers on the above forum always says (Sarah Wilson), "Dogs can change, but we have to change first." Her and Brian's books on training, are fantastic as well.