Lonely Planet (www.lonelyplanet.com/canada/alberta/banff-and-jasper-national-parks) Destination information, hotel bookings, traveler forum and more.
Parks Canada (www.pc.gc.ca/banff, www.pc.gc.ca/jasper) Comprehensive info for Banff and Jasper from the Canadian national park service.
Campground Reservations (www.reservation.pc.gc.ca) Reserve sites at Banff's and Jasper's campgrounds starting in January.
Alpine Club of Canada (www.alpineclubofcanada.ca) With 33 alpine huts and 100+ years of history, Canada's venerable mountaineering club is a godsend for outdoors enthusiasts.
AllTrails (www.alltrails.com) Comprehensive online hiker's resource.