There are a number of E-book databases that are commercially available to which college, university, and public libraries subscribe to. But whether they are downloadable or not is another question. The following are known book databases and the libraries they are available at:
ABC-CLIO Ebooks: Johns Hopkins;
Ebrary: http://site.ebrary.com/lib/alltitles/home.action?force=1
EBSCOhost:
Project MUSE: http://muse.jhu.edu/about/faq.html
ProQuest LibCentral: Johns Hopkins (JHU.eblib.com) You have to have a JHED ID and PW to access;