Appalachian Mountain Club (AMC)
"Promotes the protection, enjoyment, and wise use of the mountains, rivers, and trails of the Appalachian region"
Bureau of Land Management (BLM)
"Administers 261 million surface acres of America's public lands, located primarily in 12 Western States." Get away from the crowds and use this site as the starting point for researching unknown destinations.
National Park Service (NPS)
Great site with loads of info and high-quality maps detailing the US National Park system
World's ten classic treks (from Outside Magazine)
"Think of them as the tips of the icebergs, the peaks rising out of the clouds."