I think there are two quite distinct senses of 'intrinsic value'. We might value something for its own sake, rather than as a means to something else. We would then value it "intrinsically". But the value comes from us, the evaluators, and there is no guarantee that the object would still have any value if we didn't value it. So this brings us to the stronger sense of 'intrinsic value', which is when an object has value simply in itself, quite independently of others' attitudes towards it. The mere existence of such 'intrinsically valuable' objects - if there are any - makes the world a better place, and their destruction is a (pro tanto) bad thing.
Now, I'm inclined to think that only sentient beings can have intrinsic value in the strong sense. We are the creators of value, so without us there simply would not be any value in the world. Nothing that happens in a consciousless (I would say 'material', but that's not quite right) universe matters at all, one way or another. Hence my skepticism about intrinsic environmental value.
Nevertheless, I think that we ought to value many things - and perhaps the environment among them - intrinsically, for their own sake. Even though a pristine forest in a far away galaxy doesn't itself make the world a better place, perhaps it's something that we ought to value nonetheless. (And the conjunction of the forest with our appreciation might very well contribute real value to the universe.)
So when Brandon comments: "In a sense, the way we usually phrase the problem really makes intrinsic value a matter of taste, and the question about whether something has intrinsic value is a question of whether having a taste for that thing is an instance of good taste." I think he's captured something quite important. I might even grant that it's good taste to value the existence of distant pristine forests that no-one could ever visit. (I'm not entirely sure about that though.) But this isn't the full story, for it might be appropriate for us to value certain objects, such as truth and beauty, which nevertheless don't have intrinsic value in the strong sense that they would make the world a better place even if there were no conscious beings around to appreciate them.
Another way to see this would be in terms of the state/content distinction. Let's say value is linked to desires in some complex fashion. Sentient beings are the source of all value, for they are the source of 'desire' states. But our desires or evaluations are directed at other worldly objects. If I desire ice-cream, then ice-cream is the content of my desire. The ice-cream might then be valuable in the sense that it is valued, even though it is not itself the source of value, and indeed it would have no value at all if it were not for the fact that I valued it.