I'm using a Microsoft Natural Ergonomic Keyboard 4000. It has a great ergonomics in terms of keyboard layout and hand posture but uses very cheap key switches that feel bad and don't last long (I think I'm on my third keyboard now). Also the space bar is not engineered well.
I just wish someone would make a version of this keyboard with decent key switches for say, 90€ (the 4000 is around 36€ here).