Josh Donlan and a number of well-known biologists advocate in Nature (subscription required) the "re-wilding of North America." They suggest introducing large mammals such as cheetahs, lions, camels and elephants into the Great Plains and the southeastern US as a way to help these species out of extinction in their native areas and to revive the megafauna that went extinct 13,000 years ago in North America. They suggest establishing the first wild populations in large tracts of private lands. Landowners and visitors would benefit from ecotourism.
I hope that in case of unwanted ecological effects these species will be easier to remove than, say, rabbits in Australia. Save this caveat, I like the idea.