Sounds crazy, but has anyone ever tried a Fallbrook Technologies NuVinci hub in back with a SRAM HammerSchmidt up front? Sounds like it would be a "seamless" shifting setup with a lot of range....
http://www.fallbrooktech.com/08_Bicycle.asp
http://www.magicmechanics.com/home.php?lang=en
http://www.fallbrooktech.com/08_Bicycle.asp
http://www.magicmechanics.com/home.php?lang=en