J.S.
It looks like you've gotten a lot of good advice from the moms on here so far.
My advice may seem a little bit crazy and simple, but I am a visual learner and it really helps me to SEE things so I know exactly how to put ideas into action. The "SuperNanny", Jo Frost has written a few books that speak directly to the kinds of issues you're having with your son. If you haven't watched the show already, I would start watching "SuperNanny." She is excellent at creating schedules and setting boundaries even with the most spirited children. She is firm, yet loving. I have implemented many of her ideas in my own home and find that if you practice them consistently they work very well. The reason I suggest watching the shows in addition to getting one of her books is because I think it really helps to see her do these tactics so that you can emulate them yourself.
Anyway, if you go to Amazon.com and do a book search on Supernanny Jo Frost, her books will show up. "How to Get the Best from your Children" and "Ask Supernanny: What Every Parent Wants to Know" are good choices.
Every mother struggles with their kids behavior to some degree and even the most well-behaved children will try to push their boundaires from time to time. Finding the tools to help you when these problems arise is key. Best of luck to you!!