Most ski mountains close down mid-April, but a stellar few keep going for an extra month (or more.) Three notables are:

• Sunshine Village - near Banff in the Canadian Rockies, (pnoto above), stays open until May 19th; lots of terrain above the tree line; stunning views of mountain peaks.
• Whistler- Blackcomb BC, near Vancouver, BC: awesome ski resort with nearly a mile of vert; site of the 2010 Olympics. Blackcomb Mountain stays open until June 8th!
• Mammoth Mountain --in California, 5 hours from LA-- just won't quit; Spring Value Seasons starts on April 21 2008, and lasts 'til end of May (at least).
• Snowbird: one of the wonderful ski resorts near Salt Lake City, Snowbird stays open daily until May 11 and on weekends until Memorial Day (at least.)

^{* photo of Sunshine Village courtesy of Travel Alberta}