As the name implies, this is dedicated to military history. It includes book reviews, links, bibliographies, and articles, as well as a long list of primary sources for research on all things military.
A large collection of translated letters from Latin, written to and from women in the Middle Ages. A great source for thinking about women's literacy, learning, and religious practice. (Original Latin included)
Eurodocs is a clearing house for tons of sources and links to other collections of material. The organization is by country, but many links are less useful than they might seem. However, with a bit of digging it can yield lots of useful items.
These are some of the largest historical primary source collections on the web. The Medieval Sourcebook is particularly thorough. Many are excerpts, but there is a wide variety of full sources available.
This source specializes in women's monastic communities. While it contains a great many letters as well, it also has other documentation, including secondary sources, about women's religious groups and practices.