These are links that I visit often. Other landscape painters might find them beneficial as well.
http://community.how-to-draw-and-paint.com/profile/LouisKnight My page on a great artist community aimed at painting with skill levels ranging from beginner to highly accomplished. Lots of video demos and discussion groups.
http://www.how-to-draw-and-paint.com/index.html Many good painting tips and demos
Landscape Painters whose work I especially enjoy. Some use mainly watercolor and acrylics whereas others only oils.
http://www.robertreynoldsart.com/ Robert Reynolds an outstanding watercolor landscape painter
http://www.charlesharrington.com/ Charles Harrington a master at using acrylics like watercolor
http://www.spetz.com Gary Spetz - great watercolors
http://www.mikecallahanart.com Mike Callahan - many great landscape oil paintings in the Lake Tahoe region of the Sierra Nevadas
http://www.dougmillerart.com/ Doug Miller a fellow Washington artist who does fantastic landscapes
http://www.paulcato.com/ Paul Cato, a New Zealand artist who produces outstanding local landscapes
http://www.christensenstudio.com Scott Christensen - many great landscape oil paintings
http://www.bansemer.com/painting_demonstrations/painting_videos.htm Excellent plein aire painting videos. These have inspired me to paint plein aire with acrylics.
http://www.tpaps.com/Tucson Plein Air Painters Society