I can only speak to my western US experience.
OR: Bend, Eugene, Ashland, coast, Crater Lake
CA: most places in humboldt and mendo 'cept for Eutweeka, the eastern sierra (Bishop, big pine, ect), Yosemite and the "Mother Load" area, actually, just all of the sierra in general, the mohave desert area, San Francisco
AZ: the laws and people here kinda suck, I left for a reason. My hometown is Flagstaff, its really nice, but stay away from the cops. Prescott, Bisbee, Grand Staircase-Escalante National monument, Lake powell, Grand Canyon, Quartzsite (In winter)
UT: Grand Staircase, Zion national park, Bryce Canyon, Moab, Canyonlands NP, Mexican Hat (Ya, how many ppl have been here?), Park City, Just all of southern Utah, its awesome
CO: Boulder, Glenwoood, Durango, Pagosa springs, Dolores, Cortez, Loveland, Stay away from grand junction, that place sucks massive balls
WY: Jackson Hole and the tetons, Yellowstone, Cody, thats about it, there are some cool hot springs but you have to fine 'em yerself
, This is one of the only states in the nation that has tried to make the entire act of Hitchhiking illegal
MT: Missoula, bozeman, Butte, Glacier, Whitefish, Kalispell, Stay out of eastern MT, believe me.
ID: Cour 'd alene, Stanley, McCall, lots of awesome wilderness, watch out for Grizzlys!
NV: Legal Hookers and Vegas, the northern part has alot of great wilderness to check out.