I am planning on sticking with my G18 and adding a DX1 http://www.thinkgeek.com/computing/input/77ba/ after christmas.
so right now I am using everything from about 5tgb left on the keyboard and I remaped my num pad and insert/home/pgup section to the G keys.
Will be adding the DX1 to sit left of my g15 with who knows what, but it will be more keys!