Historical Guides and Compilations
Munich Digital Library: Rare, antique Hungarian (German, and other) texts It’s possible to find books online here (download free pdfs) that can’t be found anywhere else, online or otherwise. I have found books listed on FamiySearch, only available in Salt Lake City, on the Munich online Library for free download.
Burgenland Bunch: Burgenländers Honored and Remembered: Information on nearly 22,000 Austro-Hungarians who settled in the U.S. (You might find your great-grandparents on this list).
Understanding the 1828 Hungarian Census: Tutorial
Family Search Resources
Hungary Funeral Notices, 1840-1990
Österreich Armee Records (Mostly Austrian, but some Hungarian)