If you're a US citizen, you owe it to yourself to listen to what at least one Iraqi has to say about the war. The video's 50 minutes long but it's well worth it.
I would also like to draw people's attention to the Winter Soldier event held by Iraq Veterans Against the War. It just wrapped up today and features the testimony of veterans serving in Iraq and Afghanistan. These are voices that are rarely heard in the mainstream media. Everyone owes it to themselves to hear at least one of these soldiers talk about their experiences.
Also, most cities will have a protest or demonstration of some kind on Thursday, the 20th. If you want to make your opinion known and join with a lot of other people who feel the same way, it should be easy to find when and where a local demonstration will be.
The Real News has the best coverage of Winter Soldier that I can find.