Sam Harris has a short talk here on why he thinks "science can answer moral questions." A follow-up to some initial criticism is here, and a brief discussion of "getting an ought from an is" is here. He evidently has a book forthcoming related to all this.
While the philosophically more talented will have issues with his arguments (and with my brief discussion of this complex topic below), I agree with his main thrust. There are two key steps here: first, we include first-person experiences in our view of nature, and second, we locate the target for our (natural) moral instincts in the qualities of the experiences of sentient creatures.
1. In assessing the world, we use two perspectives-- the first-person and the third-person. On the one hand, we feel, think and form values - these are all aspects of first-person experiences; on the other hand, we work with others to determine agree-upon ("objective") facts. But there is only one world, not two. Experiences are ineliminable natural facts: they are simultaneously facts about a brain/body/environment system (viewed from the other perspective).
Now, it seems the ideal of scientific methodology excludes (or "brackets") first-person experiences, and so whether "Science" is able to assess experiences may be partly a semantic issue. But since our experiences are part of the natural world, we can explore these in a similar spirit to the conduct of science, even if we fall somewhat short of the traditional ideal (and allowing that there will be practical limits to precision). For a start, we build on the existing neuroscientific program which looks at the brain/body events which correspond with different experiential events. I would expect that in the future we can get much more sophisticated and precise compared to the tools used today.
There's just a slight but crucial difference in the stance here from that of a stereotypical materialist worldview: the experiences are not reduced to physical events: they are the same events, viewed from different perspectives. I would challenge the naturalists out there: do you really want to limit your worldview to one which excludes first-person experiences as natural facts? Doesn't this kind of reductive materialism leave the door open for the persistence of dualisms and supernaturalisms to fill the vacuum?
So, feelings, values, etc. are experiences, and experiences are natural facts.
2. But what about morals and what we "ought" to do?
Here, I have argued in the past that the intrinsic, qualitative richness of subjective experience is a good, and should be the target of moral judgments. We should favor the greatest number of high quality, robust, complex and rewarding experiences we can, and minimize low quality, degraded, unpleasant experiences. Of course this needs to be considered and worked out in great detail -- that's a huge project. We can work to develop tools to evaluate the presence or absence of the experiences we're targeting.
But even if experiences are facts and good experiences are preferred to bad, why "ought" one pursue moral goals? Can you get an "ought" from an "is"? I don't think this question has any bite. I think the evidence from evolutionary biology shows that our moral impulses are grounded naturally, among other facts about our makeup; we don't seek special explanations for our other natural impulses (I "is" hungry so I "ought" to eat lunch). It's part of our nature to seek out the best experience for ourselves, and then to seek it for others. While there is much more to be said here, too, I think it's clear that extending our circle of concern to encompass all humans and other sentient creatures is just the cultivation of a natural impulse.
So, we should pursue the study of how experiential well-being can be assessed, and use this knowledge to benefit sentient creatures (understanding how difficult and complex an undertaking this is).