BackpackingLight.com. (BPL) In 2000 this was the best site for people who wanted information about light weight backpacking. In the last few years I feel like they have been stumbling a bit (ugly UI / too many ads, etc) as they have tried to figur out how to be profitable. This site has a mix of articles that are free and availible to a paid subscription, and a forum community which is free. This is one of the best places to learn about what is on the cutting edge of backpacking, be in new materials, gear, or technique. The subscription is worth it if you are in the process of trying to lighten your load.
WhiteBlaze.net… Dedicated to the Appalachian Trail, but there are sub forums which cover topics which are widely applicable.
Trail Journals: Community site where people who are hiking long trails keep journals / diaries
Practical Backpacking… was a place with a lot of good information that is carefully moderated. I dislike the ban on including links to outside resources, but lots of valuable info was here. Seems to be offline now?
Backpacking: A Beginners Primer and other material by Paul Magnanti. Paul comes from the dirt bagging tradition, e.g. be thrifty and focus on the experiences in the field, don’t spend your time trying to find the very best gear.
Cleverhiker by Dave Collins which is primarily a gear review and trip guide site.
Adventure Allan by Alan Dixon.. a long time contributor to BPL website. Somewhat gear centric, but also some good material on technique as well.
Hiking in Finland: Hendrik Morkel site with a European take (gear and trips). His week in review is a great round-up of articles that appeared during the week in the blog-o-sphere related to outdoor activities, especially light weight style backpacking,
SGT Rock Going Light: and other pages. Gear reviews are somewhat dated but a good bit of practical advise.
Hiking Life – Cam Honan’s guide to hiking with good details about hiking all across the world.
Erin & Higs (have some great trail journals about treks in Alaska
Section Hiker: Philip Werner is one of the more prolific posted about light weight backpacking. I don’t always agree with Philip analysis, but a worthwhile site.
The Backpacker’s Handbook by Chris Townsend (now in 4rd edition) is the best general book I have found. Balanced and informative without being as voluminous as The Complete Walker. I wish I could find a shorter book that I could recommend.
Mountaineering: The Freedom of the Hills edited by Steven M. Cox, Kris Fulsaas is the classic guide to mountaineering. Pack full with useful information about mountain environments, snow techniques etc.
Hiking and Backpacking by Buck Tilton. Part of the Knack: Make it Easy series. Easy to follow with plenty of pictures. I tend to go a bit lighter weight than what this book discussions, but it’s a good, gentle introduction.
Lighten Up! Complete Ultralight Backpacking by Don Ladigin is the best book to help someone who is a traditional backpack thing about lightening their load. If I could write well, this is exactly the sort of book I would hope to write. Rather than getting bogged down in specific products which would become dated, Don looks at general principles which are easy to apply.
The Complete Walker IV by Colin Fletcher is the classic book, comprehensive, through. Great discussions about technique. Interesting discussions about gear. My only regret is that ultra-light gear (other than tarps) are not covered well.