To echo some of the other responses, I think this is the best post by Rudey that I've ever read. Writing letters is a fine thing to do, and there are also some other options, like demonstrations. It seems like the keys to success with activism are planning and publicity. For example, if you organize a march, work with the police to get the permits you need, and try to partner with other organizations to improve turnout. For large rallies, trained peacekeepers are valuable - if anyone breaks the law, it can make all the protesters look bad. Petitions can be effective too, and again, cooperating with other organizations is a great way to get signatures.
As an example, I've heard really good things about SOAW (
http://www.soaw.org). If GC'ers are close to the Columbus, GA area, it might be worth going to see their vigil this month.