All of them good but I really like #4 - 4. Coach employees to turn PCs off at night
Basically I think if you encourage employees to care about energy efficient you will see lots of improvements. To me, it's like as a kid my mom always coached me to turn off the lights to save $ but I didn't care as it wasn't my money. But then I grew older and I cared a lot about turning off my lights and PCs as it was my money and my contribution to the environment.
So maybe it is some sort of contest. Keep track of costs of electricity. And if X amount is saved...then everyone gets a day off. Or a big party. etc.