A few more good websites I have come across lately:
The Center for Science in the Public Interest: Alcohol Policy -- www.cspinet.org/alcohol/. It includes a link to BeerSoaksAmerica.org that describes itself as "a response to beer industry propaganda", including underage drinking and ads targeting youth.
The Centers for Disease Control's (CDC) "Quick Stats" on underage drinking -- http://www.cdc.gov/alcohol/quickstats/underage_drinking.htm
The Federal Trade Commission's We Don't Serve Teens -- http://www.dontserveteens.gov/
Though I've come across this one before, it keeps (unintentionally) falling off of my radar . . . International Institute for Alcohol Awareness -- http://www.iiaaonline.org/. It includes a link to the Not in Our House campaign that has information for parents, school administrators, coaches, 9th & 10th grade teachers, and students themselves about preventing adults from serving alcohol to youth.
University of Minnesota's Alcohol Epidemiology Program -- http://www.epi.umn.edu/alcohol/ -- contains data in its Quick Facts tab about youth access to alcohol; where and when youth drink; public opinion on alcohol policy; and other related topics.
Finally, if I haven't mentioned this before, I should have. The Washington State Alcohol/Drug Clearinghouse -- http://clearinghouse.adhl.org/ -- contains links to all sorts of resources including free materials you can order through the site.