MD Consult eBooks 
Full text access to medical e-books; navigate using table of contents or index; search all books or within an individual book; view and search over 50,000 photos, tables, graphs, and full-size images. 

Nursing Consult eBooks 
Full text access to nursing and allied health e-books; browse list of all books alphabetically by specialty or title by clicking on the respective text link

Contains 93 core clinical texts in a wide range of subject areas; allows online access to your essential textbooks and links between chapters, topics and referenced websites.

Site dedicated to promotion of free access to medical books over the Internet (listed by specialty).

Google Book Search: Medical 
If book is out of copyright, or publisher has given permission, program allows you to preview the book, and in some cases, the entire text; if it's in the public domain, you can download the PDF.