Have used Natura primer - excellent product. For new drywall Ben Moore also makes the Eco-Spec zero VOC primer which is noticeably thiner, but good enough for certain instances. Doesn't Zinsser have a Zero VOC version of 1-2-3 out now? Haven't used it yet but their stuff is all great.
I think I am leaning towards the Natura. It's a bit pricey though, but I think it's probably worth it. The BM Eco-Spec, as mentioned, is interesting. It is now zero-voc, and a bit cheaper than the Natura. I'll probably pay the extra $ and get the Natura though.