Mooh mentioned playing his baritone tuned CGCGCG. I keep one of my guitars in that tuning all the time. It does require some string gauge customization (a lighter 1st string at least) so it's probably best to consign one guitar to that tuning and not plan on using it for much else.

It's very similar to ADAD tuning on Irish bouzouki (the same droniness and, obviously, the same fingering), but with the advantage of having an additional string both above and below the 'zouk's range. Not having the third on an open string makes it neither major nor minor, so it works equally well for major or minor tunes. And it's easy to learn a tune in one octave and then be able to do it an octave higher or lower by just starting on a different string, instead of having to learn an entirely different fingering pattern.

Its principle disadvantage is that since I use it mainly for playing fiddle tunes, and since there aren't many fiddle tunes in the key of C, I almost always have a capo on the guitar so the first two frets are pretty much wasted real estate. I've considered having the guitar's builder, Abe Wechter, build me a short-scale neck so I can actually tune the instrument DADADA.