Okay then, I've been to:
Acadia
Arches - loved it!
Badlands
Big Bend
Black Canyon of the Gunnison
Bryce - stunning!
Canyonlands
Capitol Reef
Carlsbad Caverns - amazing!
Crater Lake - gorgeous!
Denali - enjoyed the all-day bus tour so much we did it again the next day
Gateway Arch
Glacier - my favorite!!
Grand Canyon - to the bottom and back up!
Grand Teton
Great Sand Dunes - really cool and not as well-known as it should be
Great Smoky Mountains
Guadalupe Mountains
Kenai Fjords
Kings Canyon
Mammoth Cave
Mesa Verde - lots of fun for kids
Mount Rainier
North Cascades - another one that deserves more love than it gets
Olympic
Redwood - I really loved it here, had an amazing time tracking down Hyperion, the tallest living thing on Earth, whose location is kept secret, a shame it's so remote
Rocky Mountain
Sequoia
Shenandoah - Old Rag is a great hike - but not in the rain!
White Sands
Wind Cave
Wrangell-St. Elias
Yellowstone
Yosemite
Zion
Ask away.