Here is a proposal from Freewayblogger that could let you make a difference without much more than some paint and cardboard:
Here's the plan: The day after the 2,000th U.S. soldier is declared dead in Iraq, everybody paints protest signs and puts them on the freeway. So far I've got 700 fresh recruits and another 1500 fellow-travelers alerted.
Almost two thousand dead soldiers. I weep. Not to mention all the dead Iraqis. I think that they deserve to be commemorated.