I generally distrust the "50 things you can do to [insert social good here]" approach. It seems to me that too often the steps offered are too small, too cautious to actually do much good, and that they run the risk of lulling us into a false sense of nobility.
So when I got an email recommending the Conscious Consumer Marketplace, I almost roundfiled it automatically. I'm glad I didn't, because it's actually the best of these efforts I've seen so far.
First of all, it's a readable and well-designed site. Second, it's informative: each entry includes an explanation of why changing your consumer habits in that area can make an impact, and even offers suggestions for further reading. Third, it doesn't shy away from suggesting real changes - it includes tips on doing better with the big purchases (cars, computers, major appliances) which actually make up the bulk of our impact, and adds to them smart information on things like water conservation and home energy. Finally, it gives you the fifteen most important things you can do right now, but provides access to useful information for evaluating other purchases.
Sites like Conscious Consumer Marketplace alone won't change the world very much. But making good choices is important, if for no other reason than that relatively small shifts in consumer behavior often become relatively large signals in the marketplace. Those signals, in turn, are part of what's making the emergence of transcommercial enterprises possible. And that shift, with businesses and consumers dancing together towards a changed world, is profound.
A little compendium that I like on the subject of shopping responsibly: http://mjoy.org/issues/shopping.html
I am also troubled by the idea of reducing environmentalism to checklists of easy things to assuage your conscience with. But learning to streamline your life a bit when you've been raised a fat American takes some doing. For every wasteful habit we have in this part of the world, for every wasteful item we buy, somebody has to do the legwork of creating or rediscovering a better way. And when somebody actually does that, we need to make sure we're spreading the word. Miriam, in the above link, goes to some lengths to track down some good everyday options, though I believe she's just getting started.