Its frustrating. Obama's appt. to SecAg Vilsack, while at least not a Monsanto puppet, supports GMOs and big agribusiness. Boo.
I think local politics is a good place to get involved. Write your representatives. You are a bigger fish in a smaller pond -- your vote counts! I went to a local foods dinner and met a city councilman who is a huge supporter of the local foods movement and I was really surprised to find out all he has been doing in the movement. He's even gotten federal money to work on a lot of issues, including funding ways of getting fresh food to areas without much access, which is a huge barrier for many families. We have an area with no grocery stores and just convenience stores (DelRidge for locals). They haven't been able to get any grocers to want to build there, so they are funding convenience stores to put in what they need to carry more fresh foods and produce. He even lists a lot of the info on his site for aspects of the local food movement. http://www.seattle.gov/council/conlin/food_initiative.htm
Politicians like this are who I want to support -- although I can't as I'm not in his district, but I can by following him and finding out more about local programs.
I also really agree with speaking with your dollar. Don't support Monsanto and GMO? Then don't buy a single thing they are associated with. Yes, its 'hard', especially when you are contemplating it, not doing it. If you buy anything with a major crop in it, buy organic. Check out their affiliates, you'd be surprised. Basically, don't buy major brands. Buy from companies doing good.