Energy Conservation is one o the key discussions at the moment. Here is a great way of saving energy while you search the web: Blackle.com. Blackle encourages surfers to use their site instead of google.com for, as they claim, blackscreen page helps save more energy than the white Google screen.

Dunno wether it’s true, but the idea is great!!
(Source: www.mtvsticky.com)

Some people may find that light text on a black background uncomfortable to read. Greygle offers a grey background with dark text. This allows for some energy savings while still providing a readability that some people may find easier for them. If Blackle is not something you find as an enjoyable search experience try Greygle it might be the right compromise for you.
Darkoogle.com is also doing the same thing, but their green text on black background are much more visible and readable to the eye. It reduces eye strain more than looking at grey on black background.
http://www.skinnle.com is similar, but more flexible (colors, pics, skins)
Saving energy with a dark screen is only part of the story:
1. Reduce emissions with a dark screen – only benefits on CRTs so about half the number of monitors in use today
2. Offset emissions – use ALL money generated to buy carbonoffsets and make the search process carbon neutral, or better
3. Build into your daily search routine – so even the smallest changes each and every day can add up to a big impact
The greener search engine is searchgreener.com – reducing emissions AND offsetting emissions
http://searchgreener.com