Enter Ecoimagination: A new site from General Electric (GE), the purpose of which is to raise awareness of the need for more abundant and safer sources of energy and water, and technological solutions to address those needs. Yes, it is an advergame of sorts, and yet the marketing aspect does not obstruct its entertainment value.
To get started with Seeds of Imagination, all you do is plant a seed by clicking on it. Once the seed is planted, a text entry box will appear for you to 'talk' to your plant by entering words. Some words have special meaning that will affect the growth of the plant. Try: sun, water, love, happy, fruit, etc. If a word is recognized, you will see it float up toward your plant. If not, it just disappears without a trace. You may also change the color of parts of the plant by typing in colors.
You will need to register with the site only if you wish to submit your creations to the gallery so that other visitors may rate them; however, you can do that at any point during play.
Very nice, almost tranquilizing music accompanies your efforts. A great way to relax while in front of the computer. Click.
With thanks to Rosalba for suggesting the link. =)
Update: Looks like GE took the site down and it's no longer available. We have removed all tags but are leaving the review and comments up for posterity.