Get picky on phosphates.
Pick laundry detergents without phosphates, which deplete the oxygen in water and as a result kill aquatic life. And while you're at it, buy only powdered detergent in cardboard packaging as opposed to a liquid in plastic packaging. The liquid contains water, which you already have, so it takes more fuel to ship that heavier container of detergent and water, not to mention the energy and petroleum used to manufacture the plastic container. The cardboard container also requires energy and resources to produce, but many are now made from post-consumer recycled paper and the trees they originate from are a renewable resource.
The cost-per-load comes out pretty much the same for powder and liquid, so going with the non-phosphate powders give you the chance to help the planet without any real cost to you.