The 2009 [13th] edition of the Mesopotamian Directory, has just appeared at the website of the Oriental Institute. I see in passing that one can now subscribe to their Monthly e-Newsletter by filling in a form at the OI home page. If this is the E-Tablet they have been circulating, it is well worth filling in your name and address.
The appearance of the Mesopotamian Directory makes me think about the other lists of scholars I use. Which is to say that generally speaking I don't use such directories, except under unusual circumstances. Googling almost always gives fast and reliable contact information for most people - even for some people not associated closely with institutions which tabulate the coordinates of their affiliates.
But some that I have used are:
Cuneiform Digital Library Initiative (CDLI): Who's Who in Cuneiform Studies [Yes, all deceased]
Directory of Historians of Ancient Law
Directory of Institutions and Scholars Involved in Demotic Studies
Directory of North American Egyptologists
IDAP - International Directory Aegean Prehistorians
IDE: International Directory of Egyptology
Informationen deutschsprachiger Institutionen der Ägyptologie
International Directory of Hittitologists and Anatolianists
Rencontre Assyriologique Internationale. Names and Addresses
I also use the online directories of scholarly and professional societies, which I won't list here because on the whole they are restricted to access by their members.
Are there other important directories I'm missing? What do you use to find people and places in your own disciplines? Reply in the comments below if you can.