List of all e-books available in NCBI Bookshelf (search results link in PubMed). These may come up in a PubMed search, they wll be indicated by a Books and Documents label below the citation.
Some select titles:
The R2 Library is a collection of electronic books from various publishers. These are purchased by the library, rather than licensed, so each edition remains constant. Selected new titles listed below. For a full list of titles in the R2 Library, click here.