Here are my favorties. Most of these will cover the North Rockies regions. Feel free to add more.
The RAMSDIS site is great. Realtime animations of weather data for the Western USA. This page, 16 km Polar Stereographic Water Vapor(IR3) on RAMSDIS is a real winner.
mountainweather.com is a local Jackson-based meteorologist Jim Woodmencey. Good local and regional weather. The Skier's Page on mountainweather.com is filled with information about local and regional ski areas as well as being chocked full of information on avi reports and backcountry conditions
Bridger-Teton National Forest Avalanche Center is a must read for peeps heading out to the BC. Not active for the season yet.
Jackson Hole Mountain Resort's Snow and Weather Report is a daily check. Not active for the season yet.