I agree voting is most effective, but it is not the only avenue for you to do something.
Money is also key, contribute to organizations that you believe in.
The Center for Responsible Lending was the voice in the wilderness a couple years back railing against Lending abuses and the housing bubble. They lobby the hill agressively trying to counter the big money lobbyist from banking and real estate.
There’s countless other organizations, local, state, national that try influence public policy.
Just put your Dollars where your beliefs are.
I agree, letter writing and callng your congressperson is only of very limited effectiveness. But believe it or not, they actually tally it (grunt work for a Hill intern). In a small way it may influence politicians. These folks are always trying to assess public opinion
Write letters to your local town newspaper editor, stage a sit, gather funds from like minded folks and get an ad put in the paper. Start a non-profit (you can do it very cheaply). etc..
Or just go back to watching reruns of American Idol.