The Motherload: 350,000+ online lessons, printables, and more, all teacher reviewed and rated by Lesson Planet's team of educator reviewers.
Why it's better than "just plain Googling" your topic: The wonderful world of Google, or any other search engine is too vast and you can't get it refined to as specific of criteria as you might want. You can search by grade, subject, teacher rating, resource type, teaching method, theme, technology, and more.
The history: It's been around since it's founding in 1999 by educator Jim Hurley. Over 23,000 schools world wide have used it.
The fine print: This is a cost site. Given that, I've not spent much time on it. However, depending on your budget and desire for ease in finding teaching topics (whether environmental or otherwise), the annual fee of $39.95 might very well be money well spent. (I think we've all spent close to that on a book or two that, upon up close investigation, we then discovered it wasn't the resource we were hoping for or didn't have the wealth of ideas necessary. With 350,000+ resources, and a daily breakdown around a dime, it's actually a rather cheap resource!)
The silver lining: Lesson Planet gives you a 10 day free trial. You can try it on before buying in. That's a pretty good deal, at least worthy of investigation.
Environmentally speaking alone, by clicking that topic, you've got lessons galore in:
You can also search by environmental theme: