A CRT monitor is generally the most power-hungry element in a PC, unless you have some kind of wacky copper radiator and refigeration system. Switching to LCD will doubtless save energy.
Fans consume almost no power as a proportion of the total used. The alternatives are static devices (like flower heat sinks, or lots of copper baffles - use no power), water cooling (pump etc requires power) or refrigeration (obviously power hungry).
The advantage of static cooling is that it requires no power, but it simply can't shift as much heat as other methods. Flower heat sinks and copper bits for your PC are also very cheap, and obviously make no noise.
Water cooling is nice and quiet but I am not sure how much power it uses. I think there might be several bits that use power but some of them look fairly optional.
Refrigeration is the best solution for getting rid of heat but in terms of resource consumption it's complete over-kill.
I'll bet there are a good few forums and sites that deal specifically with comparisons of power consumption for things like this, so I'd suggets looking for benchmark tests of popular cooling solutions.