This morning I came across a great lesson aimed at engaging students in the democratic process called Writing Letters that Matter from The Polliwog Journal. I might tweak it a bit and do something similar with my students. I've also been considering doing a mini unit on editorial writing with my freshmen, with part of the expectation being that we will submit the editorials to our local newspaper.
In my journalism class, students write and submit an editorial each quarter. So far, four of them have been published in the paper's Student Opinion Page. Whenever possible, I try to incorporate some type of publishing component with the writing assignments I give students. Sometimes the audience is just the other students in the room, but this alone helps provide internal motivation for them to put a bit more effort in, knowing their writing will be read and heard by others.