Roko has a nice blog post about transhumanism and atheism on his Transhuman Goodness blog over here.
I made a comment that is long enough to merit repeating here (with additions and some corrections to typos). It may not make complete sense outside of the original context.
On the general relations between transhumanism and the naturalistic worldview, I do think there's some synergy, although I'm a philosophical naturalist before I'm any sort of transhumanist. I don't think that naturalism necessarily leads to a full-on commitment to transhumanism ... more to a realisation that many of the popular objections to it are bogus. In fact, it's possible to be committed to some forms of transhumanism from within at least some religious viewpoints.
It's long struck me, though, that if we see the current human form and its attendant capacities as massively contingent evolutionary outcomes, rather than as the products of a divine plan, we will naturally wonder how they might be improved (improved from the viewpoint of our existing values). A naturalistic viewpoint that emphasises our evolutionary history and the imperfect, jerry-rigged outcomes of evolution, will tend to be friendly to transhumanist aspirations, at least in principle.
On the other hand, I can't imagine transhumanism ever playing the role in my life that religion plays in many people's lives ... and perhaps there I am at least a bit different from some of my transhumanist friends. For me, that role is played by, if anything, relationships, literature, art, and philosophy.
I defend transhumanism up to a point, and I do my best to encourage rational discussion of it ... and I think all this is important! But I'm not focused so much on what transhuman technologies might do for me, personally. E.g. I'm on the wrong side of 50 now and not likely to belong the first immortal generation. It's more the ideas that interest me than something more concrete than I, personally, am going to get out of it.
On the gripping hand, I do thank goodness (but not a deity) that I live in a time when 50 really is pretty much the new 30 ... if I go to the dentist, the orthodontist, the endodontist, the periodontist, blah, blah, exercise a bit, and generally take advantage of everything that modern living has to offer, I'm in a situation, here in a rich and relatively enlightened country, where I can look, act, think, and feel nothing like the 50-y.o.'s of past generations. (Have a look at some 19th century photos and see how blokes in their 40s look, to our modern eyes, like men in their 60s or 70s.) I realise how lucky I am compared to people who lived in less fortunate times, or who live in less fortunate countries or less fortunate personal circumstances, but there's no way that I'm going to object to this kind of social development ... and may it accelerate!
As for naturalism versus the lure of religion ... now I come to think of it, I don't think I ever found the promise of heaven remotely plausible, even in the days when I was supposedly a Christian. I find the naturalistic worlview liberating, because it lets me focus on a rational understanding of the world I find myself in, and on working out what I personally value, not on whatever is taught in some ancient tradition - however much reinterpreted - or ascribed to some imaginary being.