Also, if you decide to go for a road trip, this site is great for finding obscure attractions and silly museums. It's a lot of fun - my favorite thing I found from this website was Foamhenge. A Stonehenge made out of foam. http://www.roadsideamerica.com/
We are going to Las Vegas ourselves. But I'm from Michigan and I have to say that if you haven't been it's lovely in the summer (the only time of year it is!) Check out the Traverse City Area (wine country and Land of the Cherries!) or the Pictured Rocks in the Upper Peninsula.
Hawaii is still the USA! But I'm biased. Assuming you don't want that, I grew up in Colorado and lived in Arizona for some time as well. There are some amazing places in both states with so much beauty! I lived in Flagstaff, AZ which is in the mountains (so highs in the 70s and 80s in the summer...not like the desert) and there are these really nice cabins you could stay in and the Grand Canyon is nearby, then you could take road trips up to Utah, and visit things like Antelope Canyon, Bryce, Zion, Monument Valley, and maybe even Vegas if you want.
In Colorado the rocky mountains are beautiful. My sister had her honeymoon in Glenwood Canyon and Keystone. Steamboat and Estes Park are also beautiful. If you have any questions about any of these places let me know!