The Yukon IMO. Population is less than 100K, and yet its frickin HUGE. Lots of open wilderness, mountains, lakes, etc. Just like Alaska, which I think is the coolest US State.
Also, at least during the summer, and small portions of fall and spring, the Yukon is pretty temperate. (I visited the Yukon in June of 1998, and it was quite comfortable with shorts and a T-shirt on.) That is a place I look forward to visiting again some time in the future, at the very least, driving through the Yukon an a massive huge road trip to Fairbanks (from Chicago.)