There are several hundred open access textbooks available from Springer here and a number of these are medicine, health, psychology and social science oriented. Make sure you untick the box for “preview only” or you’ll get ebooks which aren’t open access.
ebooks direct has a number of medical books available on an open access basis including areas such as emergency medicine, immunology, pharmacology and physiology.
National Health Library & Knowledge Service. Health Service Executive. Dr. Steevens' Hospital, Dublin 8. Tel: 01-6352555/8. Email: firstname.lastname@example.org