Rhodes University Academic Libraryis a great historical research site that provides resources for a variety of histories. I suggest investigating the European History link and it will provide you with a wealth of research options.
Trenches on the Web is a fantastic World War 1 reference site that offers pitctures, letters, and poetry from the soldiers of World War 1. It is suggested you scroll down the page and enter the sites reference library to begin exploring.
World War I Document Archive- This is a collection of World War I documents and texts from Brigham Young University. There are a variety of options at the bottom of the page that range from pictures, commentaries, and even has a biographical dictionary Trenches on the Web