Where There is No Doctor is likely the most widely distributed health education book in the world. It was written by David Werner, a biologist and public health professor, who was doing health care work in Mexico. He founded The Hesperian Foundation which distributes free versions of this book as downloadable PDFs on their website. The Hesperian Foundation has since created many other books that contain great information.
I highly recommend having these books as part of a general home self-care medical library. While not as necessary in the developed world where we have pretty easy access to healthcare... and I am especially comparing us to developing countries... we never know when we may be faced with a Hurricane Katrina or a 2004 Tsunami and our access to care suddenly becomes very limited or just plain gone for an unknown amount of time. I am really not an alarmist, but I do try to hold true to the Boy Scout motto: Be Prepared.
Here are the links to download these great resources:
Where There is No Doctor
Where Women Have No Doctor
A Book for Midwives
Where There is No Dentist
Also, here is their main download page. Follow this link to find these books in Spanish as well as a few other free downloads.
Finally, if you are interested in having the whole book, you can follow the link at the top of the page to purchase one from Amazon.