The classic two weeks: New York, Washington, Orlando
Days 1 to 5: New York City (museums, Broadway, neighbourhoods). Days 6 to 7: Amtrak to Washington DC (the Mall, the Smithsonians). Days 8 to 14: fly to Orlando for the theme parks, with a Kennedy Space Center day.
The western parks loop (10 to 14 days)
Fly to Las Vegas, then loop: Hoover Dam, Grand Canyon, Monument Valley, Arches, Bryce, Zion, back to Vegas. Add Death Valley or the Grand Canyon's North Rim with more time. Spring and fall only; summer is dangerously hot.
California coast (7 to 10 days)
San Francisco (3 days), Highway 1 through Big Sur to Monterey, Santa Barbara, Los Angeles (3 days), San Diego (2 days). The drive is the destination.
The Deep South music trail (7 days)
Nashville (2 days), Memphis (2 days: Beale Street, Sun Studio, Graceland), Natchez Trace to New Orleans (3 days).
New England fall (7 days)
Boston (2 days), the Berkshires, Vermont's Stowe and covered bridges, New Hampshire's White Mountains, Maine's Acadia (2 days). Late September to mid-October.