Amazon offers a fair number of ebooks for free for limited periods of time on their site. Some of those are useful/applicable to this forum and this thread is intended to collect them.
Here is one right now that is rated highly: [ame="http://www.amazon.com/NOLS-Wilderness-Medicine-Edition-ebook/dp/B004WQSM5S/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1338636228&sr=1-1"]NOLS Wilderness Medicine: 4th Edition[/ame]
Here is one right now that is rated highly: [ame="http://www.amazon.com/NOLS-Wilderness-Medicine-Edition-ebook/dp/B004WQSM5S/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1338636228&sr=1-1"]NOLS Wilderness Medicine: 4th Edition[/ame]