What kind of riding do you do and how dirty is everything else? For a bike ridden off road in mud or through lots of moist loose dirt, a pressure washer might be appropriate for the gears and much of the rest of the bike.

For road bikes, I use moist towelettes that come in bottles similar to clorox wipes and after they've been used on the frame, I roll them up or twist them and then see-saw them between the cassettes.

Though, I'm not going for spotless like GlennR . I'd have to make sure I hide my bike in shame if I knew he was around. However I admire those that do take the time to clean that well.