See the links below.
Mr. James Swan devotes considerable time on his blog site to Luther's works, documenting where to find them in digital format on the Internet. A big thank you to Mr. Swan. Here is his latest post, with a very helpful index of the materials that are now available via a massive digitation project at Calvin College:
Here's just a quick follow up to Carrie's post on the new Post-Reformation Digital Library. The section on Luther is excellent. Some the texts are versions released during the 16th century. Helpful pdf links to an organized Google Books D. Martin Luthers Werke (Weimar, 1883-) is also available, as well as other resources:
D. Martin Luthers Werke (Weimar, 1883-)