The main usage of energy in a Dishwasher is in the usage of hot water and the electricity used by the heating element in the "heated dry" feature.
While a few may be wondering, "Why can't I just wash dishes on "cold" like I do my clothes?" The big difference here is that most people don't eat their clothes. To properly clean your tofu burger plates and organic beer mugs, you'll need to wash the dishes around 140 deg. F (which is why you should ensure you hot water heater can deliver water at this temperature, unless you have a booster heater on your dishwasher).
However, a very simple method to save some energy here aside from the hot water, is to never use the "heated dry" feature on your washer. "But how will my dishes get dry!" you ask. Simple. Just open the door when your dishes are done!
Doing this allows the steam that has built up in the washer to escape into the air, opposed to collecting on your flatware, thus removing the need for "heated dry". Now, this does require one extra step (opening up the door when the "done" buzzer goes off) but I think you can handle that. Also, this will cause the temperature in the kitchen to rise slightly, which helps in the winter but may need a window-opening in the summer.
For more info:
The California Energy Commissions thoughts on Dishwashers