In no particular order ..
Chicago Free Zoo
Painted Desert in Arizona
Friends' RV park in Colorado
Pacific Coast Highway and US 101. Drive from San Diego to Port Angeles in Washington using a series of local, state and US highways like the 101. Plenty of man-made attractions along the way like the Space Needle, Monterey Bay Aquarium, the surf at San Luis Obispo.
Route 66 - Start at Santa Monica Pier
Oregon Trail starting in Independence Missouri and ending in Oregon City, Oregon
Blue Ridge Parkway - 469 miles across Virginia and North Carolina following the Appalachian mountains. Goes from Shenandoah National Park to the Great Smoky Mountains Nation Park in the south. Plan on snow if you go in late fall, winter, or early spring.
Great River Road through 10 states, 3000 miles. Follows the Mississippi River from its source in Minnesota to the mouth in Louisiana. National Scenic Byway so it has all tourism amenities, interpretive centers, and other attractions. Expect some differences in terrain such as hills and forests of the Driftless Area in the north and the Ozarks farther south, to the plains and farmland of Iowa and Illinois.
Time sensitive events
Frozen Alligators @ Shallotte River Swamp Park in North Carolina - exactly what it sounds.
The Wave in Arizona in Utah-Arizona border. 5.2mi round trip hike, requires permit. Good for Spring and Fall.
Jazz Fest in New Orleans
Indianapolis Motor Speedway in Indiana over Memorial Day Weekend - Carb Day, the last day of practice before the race includes parties and concerts on the track's infield. Also the 500 Festival, a month long party that includes a mini marathon, a parade, the Snakepit Ball on race eve, and more. Some lots have electrical hookups.
Great Campgrounds for Skiing and Snowboarding