I stumbled across an interesting post recently as a result of an internet search: Modern Physical theory as a basis for Ethical and Existential Nihilism.
This is fairly similar to the sticky situation I find myself in, although I'd say I've gone a little further in my own thinking than the guy who wrote this. Basically no logical justification for moralism. I also don't know as much about the theories that he talks about, although I've at least *heard* of all of them.
The 'everything-list' forum looks pretty interesting.