The first two links below are world-wide portals to archival materials.  The remaining resources focus on using the archives and the specialized information you need to take advantage of their rich resources.

So what do you ask for when you get to the archives: papers, books?  As with most other fields the terminology is highly specialized and you need to be familiar with it before you get there.  There are alot of very useful sources for this.  Many are actually in the archival guides.  Below are two that you might find helpful.

http://www.iias-trieste-maribor.eu/index.php?id=68&L=1

http://home.interlog.com/~moslon/olga/glossary.htm