I think bamboo is a good up and coming fabric. Bamboo grows like a weed so it's pretty sustainable and I'd say it's pretty durable as well. I've got some bamboo work socks a couple of years ago and they are still going hard. Super soft and comfortable too.
I don't think there are heaps of options available in terms of shirts and shorts, pants, etc yet. I'd say the ones that are out there would be more expensive than polyester or even cotton. But hopefully as the industry grows they get cheaper.
Edit: I think bamboo breathes really well too. Well it at least seems to with those socks I have. So it could be a good fabric for hot weather too.