This fellow has ship plans of some early 1900s ships..
http://www.viribusunitis.ca/plans.html
Christian also has plans for many:
http://www.christian-schmidt.com/
good references here:
http://www.cityofart.net/bship/dreads_directory.html
general sourses but plans as well:
Great War at Sea;
http://www.gwpda.org/naval/n0000000.htm#swt
Blue prints for free here:
http://www.the-blueprints.com/blueprints/
ONI (office of naval intelligence) WWII including some WWI ships:
http://www.coatneyhistory.com/drawings.htm