Via John J. Miller, one alternative to congressional representation or retrocession for DC:

End Federal Taxation: Given its exclusive power over the District, Congress could abolish federal income taxes on District residents, providing a powerful solution to the city's "taxation without representation" complaint. This is a reasonable compromise and fully within Congress's powers. Other non-voting territories, like Puerto Rico, do not pay federal income taxes for similar reasons.

I bet DC residents would take it. And as Miller remarks, it'd do big things for local property values. Of course, do this and next thing you know people around the country are clamoring for the right to give up their vote in exchange for not paying income taxes. Maybe some of the blogosphere's libertarians can start organizing around that proposal.

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