Pacific Crest Trail Association - When it comes to where to start getting information about the PCT, there's no better source than the PCTA. Find out about the trail, how to hike it. While you're there, you might as well join the PCTA, purchase the guides and maps and maybe a video or two.
Appalachian Trail Conference - A great source of information on the Appalachian Trail.
Continental Divide Trail Alliance - Updated information about the happenings on the CDT.
Continental Divide Trail Society- The best source of Guidebooks for thru-hikers on the Continental Divide Trail .
American Long Distance Hikers Association West - ALDHAW Find out about the Triple Crown of Hiking.
Appalachian Long Distance Hikers Association - ALDHA - While this site is centered around the Appalachian Trail, it has useful information for any long distance hiker
Ultralight Backpacking Sites
BackpackingLight.com - One of the best online resources for trimming those extra pounds from your pack. Full of tips and techniques on lightweight backpacking.
The Lightweight Backpacker - One of the first and largest sites for getting information on lightweight backpacking. You can read reviews, find out about the latest equipment, get equipment list and order some of those rare items not carried by the major outdoor suppliers.
Ultralight Gear Manufactures
Anti-Gravity Gear - Excellent selection of UL gear from stoves to food.
BackpackingLight - Wide selection of gear, shelters, Spectra cord, clothes.
Feathered Friends - Makers of some of the best down bags available. I've got one and love it!
Gossamer Gear- Glen Van Peski has created some of the lightest and most innovative packs and shelters available.
Hennessy Hamocks - The premier backpackers hammock available.
Jacks 'R' Better - Excellent selection of down quilts and hammocks.
Mountain Laural Designs - Excellent source for ultralight durable packs and shelters by Ron Bell.
Nunatak - Excellent selection of UL Quilts. I've got one!
simBLISSity - A selection of unique UL products.
Tarptent- Henry Shires' line of Ultralight tarptents.
Trail Designs- By far the best alcohol stove cook set on the market. Beautifully designed and engineered.
Ultralight Adventure Equipment - Supplies excellent lightweight packs for Long Distance hikers.
Lightweight Backpacker Homemade Gear - A selection of gear that you can easily make.
Thru-Hiker.com - Includes a selection of gear that you can easily make, along with numerous tips.
Outdoor Wilderness Fabrics- Supplier of fabrics, (including 1.1oz Sil Ripstop) hardware, patterns etc for the person who wants to put together their own outdoor gear.
Seattle Fabrics - Specializing in outdoor fabrics, (including 1.9 oz Silicone Nylon Ripstop) hardware, and patterns.