Syriacologist Steven Ring tells me that Brigham Young University and the Catholic University of America have scanned a bunch of Syriac publications and placed them online:
http://www.lib.byu.edu/dlib/cua/
These are in google books-like form, although I haven’t worked out yet how to download any. They include the Syriac of Eusebius Theophania, the Bibliotheca Orientalis of Assemani, and much much more. The collection includes manuscript catalogues and publications like Inedita Syriaca, containing Syriac versions of pagan texts, which I have sought in vain. Very, very useful to have.