Treehugger. Treehugger adds more than 30 posts a day on topics related to environment, health, and sustainability. This is how they describe themselves:
"TreeHugger is the leading media outlet dedicated to driving sustainability mainstream. Partial to a modern aesthetic, we strive to be a one-stop shop for green news, solutions, and product information."
Note that Treehugger is a Discovery company, which gives it substantial resources to keep it going. Also keep in mind that it is part of the Discovery conglomerate, which is essentially an entertainment company.
With as many posts as they put up, it can be overwhelming. They offer a dozen subtopics to help screen for those posts that are most interesting to you, including "Cars + Transportation," "Travel + Nature," "Business + Politics," etc.
Beyond its postings, Treehugger also includes forums, polls, games, and a series of guides on how to "green" many aspects of life, such as weddings, cars, gift-giving, renovations, etc.
Much of the content is relatively short, without significant in-depth detail, but they occasionally point you to more complete resources.
It's definitely worth keeping an eye on Treehugger, mainly for its ability to find interesting stories from across the sustainability spectrum.