This isn't the first portable GameCube mod that we've seen, but it might be the prettiest: a backlit LCD screen, perfectly integrated controls, fingerprint-less plastic, and a design with hints of original Game Boy. There's just one catch, though.
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ModRetro Forum member Techknott's GameCube Portable was built in a rush, and there are unfortunately no batteries at the moment. So while it's still portable in the sense that you can carry it around with you, you'll need an AC adapter to make it hum.
Still, though, it's a mod that wins on looks alone. And Techknott promises a version with "the works" when he's got a little more time to work on it. Or might I suggest a Wii Portable? Eh? Eh? [ModRetro Forums via Slashgear]