Must see:
Yosemite
Grand Tetons (and Yellowstone)
Utah (practically the entire state - Moab, Capitol Reef, Escalante, Zion, Bryce)
Grand Canyon (only been to North Rim - spectacular)
Tahoe, and countless other spots in the Sierra
Death Valley (winter only)
California coast (Cambria, San Luis Obispo, Pismo Beach, Big Sur, Point Reyes, Bodega Bay, Jenner, Ft. Bragg, Mendocino)
Oregon Coast (Astoria, Cannon Beach, Newport, Florence, Brookings)
Crater Lake (OR)
Northeastern Oregon (Baker City, Enterprise, Joseph, Sumpter)
Mt. St. Helens (WA)
Mt. Shasta (CA)
Mt. Lassen (CA)
Mt. Rainier (WA)
Sonora Desert (AZ)
Other ideas that are on my list but that I haven't yet seen:
Monument Valley
Dinosaur National Monument
Black Hills, Mt. Rushmore
Glacier Park
Independence Rock