"Green" Oldies: What Do You Think?

Hey folks! My question this week stems from my enjoyment of the Beach Boys' "Don't Go Near The Water," which I'm listening to as I write this. What's your favorite environmentally conscious oldies song? It can be serious or humorous, direct or metaphorical. What would you blast on Earth Day (or any day when you're feeling particularly "green")? Let me know what you think!