A recent e-mail discussion reminded me that if I could choose only one new library to start digitizing its holdings, my first choice without question would be the Staats- und Stadtbibliothek Augsburg. It not only has a large collection of fifteenth- and sixteenth-century printed books, but a relatively large percentage are also unique items unavailable anywhere else, at least to judge by what I found while working on Printing and Prophecy. The great thing about it is that you can go to Augsburg and find editions no one else has looked at in decades or centuries, if ever, and discover fresh material that no one else has written about. The frustrating thing is that it's only in Augsburg, and if you don't have money for airfare, you're out of luck.
To give just one example, following the multi-generational, long-distance dispute between Johannes Virdung, Georg Tannstetter, Aegidius Camillus, Johann Carion, and Andreas Perlach that played out between 1520 and the early 1530s requires a visit to Augsburg because it is the only library with copies of some of the prognostications and invectives in which it was carried out.
Unique Augsburg items include:
VD16 ZV 13593. Georg Tannstetter, Practica for 1519.
VD16 T 171. Georg Tannstetter, Practica for1524.
VD16 ZV 24183. Georg Tannstetter, Practica for1525.
VD16 ZV 24181. Johann Carion, Practica for 1519.
VD16 ZV 25789. Johann Carion, Bedeutnüs und Offenbarung, 1531.
Not in VD16: Johann Carion, Bedeutnüs und Offenbarung, 1534.
Not in VD16: Aegidius Camillus, Practica for 1531(Vienna: Hieronymus Vietor; cf. VD16 ZV 24784)
For any major research project, I just assume I'll need to visit Augsburg at some point.