This is a very helpful resource for students of Luther, particularly if you want to read a quote in the secondary literature in context - an online index of the St Louis, American and Weimar editions of his works. Many thanks to the website author for making this available.
While on the subject of free online Luther resources:
If you want to check a quote or citation in the Weimarer Ausgabe you can do so here.
And here is a handy list of links to Luther's writings in English translation online.
And here is an index to the English edition of Luther's sermons.
For general readers, here is a free download of Roland Bainton's biography and here is an American PBS documentary, 'Martin Luther: Reluctant Revolutionary'. Like all popular accounts of Luther's life aspects of it are questionable, including the title. Theologically speaking, Luther could only be regarded as a revolutionary from the perspective of a diehard traditionalist Roman Catholic, while historically speaking by no means can all that stemmed from the Reformation period can be attributed to Luther. In particular, the idea that Luther is responsible for the break up of the putative unity of the Western church is a gross, unhistorical simplification. And, as suggested in the previous post, the homogeneity of the church bodies which arose out of the Reformation period has in the past been overstated; we should really speak of "Reformations" rather than "the Reformation". But there is interesting commentary from the likes of Anglican theologian Alister McGrath and it does attempt to present Luther in a broadly historical perspective. The production values are excellent.