I've mentioned archive.org before, but have just found a new gem, so thought it worth reposting.
Archive.org is a collection of scanned-in out-of-copyright texts.
Works related to calligraphy and paleography that I've found include:
An introduction to Greek and Latin Paleography, Thompson, Edward Maunde, 1912
Examples of Greek and Latin texts intended to teach history students how to read original sources - very useful selection and commentary about period writing with exemplars (but no instructions on reproducing them, only on writing them). Great examples, with comments about abbreviations and curiosities of individual documents.
Edward Johnston's books - he helped revive calligraphy as a craft at the turn of the 20th century in England. He's a raging snob about lettering, defining the Roman letters as the purest form, and everything else is 'confounded and disguised' especially the hated Lombardic capitals.
However he has very useful sections about cutting quills, setting up your own slope, gilding and burnishing gold, and penwork, including Roman and Romanesque capitals.
Writing & illuminating & lettering, 1906
Manuscript & inscription letters for schools & classes & for the use of craftsmen (1909)
David Harris' Art of Calligraphy, one of the 'workhorses' of the Society scribe, with splendid clear how-to instructions for most hands we use.
It's under an attribution, non-profit, non-derivative license, rather than being out of print.
This last one is a great find - I can now refer people to the actual book, rather than just saying 'go look it up'.
SO: happy browsing, and if you find other similar treasures, please let me know!