After praising the Virginia Law Review and the Duke Law Journal for posting their issues online -- and naively assuming that they were the first Top 20 journals to do that -- I got lots of e-mail from editors at other journals, saying they did the same: Columbia, NYU, Penn, and Yale, plus also American, Buffalo Criminal, Indiana, NYU J of Legislation & Public Policy, Wash U, and of course various tech law journals. News to me, and I expect news to many others.
Unfortunately, I couldn't find a comprehensive directory of all the journals that have online content; the Library of Congress list is underinclusive, the Jurist list is overinclusive, and the findlaw list isn't up-to-date. There's also no good search engine that I could find that just searches through law review articles, and does so comprehensively; google seems overinclusive, and findarticles.com seems underinclusive.
I suppose that's just a reminder that pay services which are in this business (WESTLAW, LEXIS, HeinOnline) do tend to be more comprehensive than amateur or free services, or ones that don't focus on law.