Milton Friedman advocated an interesting, soft version of the minimum income called the negative income tax.
I like that version because it makes more clear that you don't have perverse incentives with respect to working: you never get more money by working less. The $20k/year is guaranteed unconditionally and you can supplement it with a job if you choose.
So this idea is actually not that far out for the US, at least.
I should also point out that the FairTax is primarily supported by conservatives at this point, though from my point of view, liberals should be even more supportive.