Here are some valuable resources for Letterpress printing:

Briar Press the best portal for equipment classifieds, discussion area, downloads – ESSENTIAL!
NaGraphics great resource for printing supplies, Fritz Klinke owner, best for Vandercook supplies
Boxcar Press excellent site – fully investigate all the areas
AAPA excellent resource, especially the Resource Guide
Five Roses important information resource
Vandercook Press Vandercook blog
APHA become a member of the American Printing History Association

Some Books:
Burke, Clifford. Printing Poetry: A Workbook in Typographic Reification. San Francisco: Scarab
Press, 1980.
Chappell, Warren, Bringhurst, Robert. (2nd ed. rev.) A Short History of the Printed Word.
Vancouver, BC: Harley & Marks, 1999. http://www.hartleyandmarks.com/
Dodd, Robin. From Gutenberg to OpenType. Vancouver, BC: Hartley & Marks, 2006.
Dowding, Geoffrey. Finer Points in the spacing & arrangement of Type. Vancouver, BC:
Hartley & Marks, 1995.
Gordon, Bob. Making Digital Type Look Good. NY: Watson-Guptill Publications, 2001.
Lawson, Alexander. Printing Types: An Introduction. Boston: Beacon Press, 1971.
Mitchell, M. and Wightman, S. Book Typography: A Designer’s Manual. Marlborough, Wiltshire,
UK: Libanus Press, 2005. Get from www.oakknoll.com
Morison, Stanley. A Tally of Types. Cambridge, UK: Cambridge U. Press, 1973.
Rummonds, Richard-Gabriel. Printing on the Iron Handpress. Oak Knoll Press, 1998.
ISBN 1-884718-40-x paperback. Most of the information is relevant to any type of
letterpress printing.

Printing Handbooks:
Hoch, Fred W. Handbook for Pressmen. NY: Fred W. Hoch Assoc., 1936. Many editions
over the years.
Lange, Gerald. Printing Digital Type on the Hand-Operated Flatbed Cylinder Press – 3rd ed.
Go to:
http://BielerPressxi.blogspot.com/ for details. Important for photopolymer
platemaking and printing on the Vandercook cylinder press.
Mills, George. Platen Press Operation. Pittsburgh, PA: Carnegie Inst. of Tech, 1959. ESSENTIAL.
Check with
NA Graphics for availability.