For organizers on the go, the American Friends Service Committee–founded by the old-school peacenik Quakers–has assembled a succinct primer on the impact of a war in Iraq: http://www.afsc.org/iraq/guide/Default.shtm.
If you want to settle in for a more thorough read, try the Institute for Public Accuracy, http://www.accuracy.org/. IPA staff is led by sydicated lefties Norman Soloman and Sam Husseini, formerly of the Arab Anti-Discrimination Committee and the media watchdog, Fairness and Accuracy in Reporting (FAIR).
A clean interface with a clear message: no retaliation abroad in the name of justice at home. Not in Our Name (NION) got its name from the statement made by a September 11 victim’s family against the bombing in Afghanistan. NION, which is backed by Congresswoman Barbara Lee, Martin Luther King III, and death row activist Mumia Abu-Jamal, has organized major efforts in New York and San Francisco. You can sign its beautifully articulated \"pledge of resistance\" in 18 languages. Its parent site http://www.unitedforpeace.org/ offers information on events elsewhere in the country.
Propelled by the Clinton impeachment debacle, a pair of Silicon Valley do-gooders put together an electronic people’s campaign to urge congressional leaders to register their grievances and \"move on.\" Since then, the MoveOn PAC has mobilized thousands of people and thousands of dollars with their fairly mainstream, red-white-and-blue, pro-democracy campaigns to untangle the 2000 vote count, to unveil Cheney’s role in Enron, and to counter U.S. militarism since 9/11. If you’ve got the bandwidth, check out their new-fangled version of the Vietnam-era little girl with daisy TV ad. They’re geared toward the \"exhaust all diplomacy\" approach.
For organizing materials, http://www.postersagainstwar.org/ has set up a clearinghouse of free, downloadable, and printable anti-war fliers from various organizations.
If you’re looking for protest music to spice up your event, http://www.zmag.org/songs/songarchive.htm has a limited array of lyrics from latter 20th century American artists, from Gil Scott Heron to Billy Bragg. For a broader scope of U.S. songs, browse revolutionary songbooks and audio clips that high school teacher, Nicholas Bonotto, has arranged by historical era at http://dons.usfca.edu/npbonotto/protestsongs