Andrew recommended a website to me for easily finding out the publish dates of the material of popular authors. The website is based out of the U.K. Check it out here: http://www.fantasticfiction.co.uk/
It looks like a very simple database, but it has everything the author has ever published, including materials written under pen names if the name is known to the public. It also endeavors to list works about the author, as well as books the author recommends. Interesting stuff and definitely worth taking a look at when you get a chance!