I found an interesting site covering World War 2 in Yugoslavia. It has information on all sides involved in it (restricted to their involvement IN Yugoslavia).
http://www.vojska.net/eng/world-war-2/
It offers different languages, for most Croatian, English and Serbian, but also Italian, German, Russian, Czech, Bosnian etc.
You can often find informaiton on hardly known topics, but sometimes you might get surprised about some missing stuff, which can sometimes be found then under another lanugueage. For example, a biography of Josip Broz Tito is only available in Bosnian (and there it is a long and detailed one), while in English, he is only mentioned.
It also has some information regarding other stuff, modern armies for example.