Alex Berenson's book Tell Your Children has provoked a lot of discussion concerning the potential dangers of marijuana. (See this favorable review from Stephanie Mencimer in The Washington Monthly here.) I haven't read it, but I gather a Berenson has come in for some legitimate criticism for misrepresenting the research he cites. Of course, the subject excites a lot of passion and pre-judgment on both sides.
Below pediatrician and medical school professor Dr Aaron Carroll, whom I cite a lot here, presents what strikes me as a generally balanced view (though I'm not sure he's right that alcohol is as dangerous as he implies).