I'm picking Wyoming for Yellowstone, Grand Tetons, Cody and the ride through Utah and Colorado to get there.
However, where I live in California is damn hard to beat. In the dead of winter I can ride up the coast to Malibu for breakfast, and then ride the Santa Monica mountains all in a day. Stop at The Rock Store and maybe meet Jay Leno, or Arnold. Further up the coast is Morro Bay, Cambria, all the way up to San Francisco. Cut inland at Santa Cruz and you can take the 9 as it winds through small towns in the Santa Cruz mountains stopping for lunch at Alice's Restaurant. Keep going up the coast and you'll hit the California Redwoods and Oregon.
Then there's the Sierra Nevada mountains. A nice ride up 395 will bring you to nice small towns, and then Yosemite. From there you can take Hwy 49 and stop in all the Gold Rush towns before ending up in Lassen Volcano National Park. If you want to stay local ride the 2, Angeles Crest Hwy. You can go to Lake Big Bear and end up in Wrightwood for lunch. Cross over the 15fwy and continue on to Lake Arrowhead where you can drop down into Palmdale and Lancaster (really not much there) or drop down and go to Palm Springs. I haven't even touched on San Diego, Palomar mountain, and Ortega highway.
All of this depending which way I turn coming out of my driveway.