The Geography & Map Division at the Library of Congress is constantly adding digitized versions of historical maps to their online collection/database.
Every month the G&M Division publishes New Maps This Month!, a roundup with direct links to each new addition along with basic bibliographic data.
Last month more than 50 maps were made available online
You can access the April 2014 update (11 pages; PDF) here. We’re also embedding a full text copy below.
Previous issues of New Maps This Month! (back to May 2011) are also available.