A simple solution for the vast majority of domain squatting: just charge a "property tax" of $100/year per domain. That's not an outrageous amount for a real user, but it makes the "buy a zillion domains and park them until the Big One comes along" business model no longer mathematically sound.
Any organization that's sufficiently large they don't care about the small incremental income. That is, anybody who's not a domain registrar.
I'm not a U.S. citizen, but the U.S. federal government would fit the bill just fine, and would be the obvious (though inevitably controversial) group to do it for .com, .net, and .org, ie. the problematic ones.
