I would love to go back to Alaska and the Yukon. I think you could spend your whole life exploring places up there.
I love South America and the fact that there are still some truly wild places down there (eastern slopes of the Andes from Colombia to Bolivia) that are like what North America was back in the 1830s, unexplored areas with no dirt roads, no reliable maps, indian tribes that have very little or no contact with the outside world, and the occasional roving group of desperados to try and avoid. I know that does not sound like a great place to take the family on vacation but the feeling of being in truly wild country several days in a canoe or on foot from the nearest town is an incredible feeling. Most of the guides in river towns like Leticia speak several indian languages as well as Spanish/Portuguese and trade with the more remote tribes, bringing machetes and pots to trade in exchange for bows, spears, blowguns, and illegal items like jaguar skins. Kind of like I imagine lots of the mountain men did who felt as home in a Cheyenne village as they did on the streets of St. Louis.
As far as the lower 48, I love some of the canyon country in Utah, far enough away from Moab to get away from the crowds, and lose your self in some canyon in the San Rafael Swell or the Blue Mountains. I also love the Wind Rivers, the Rubys, and some of the places down in the Animas mountains in the boot heel of New Mexico.
I hope to explore the Frank Church country some day.