Randall Holmes says he has a proof of the consistency of NF relative to ZFC (and in fact something weaker, I think). He's said this for a while, he's published a few versions of his proof (mostly different in presentation in the interests of clarity, rather than patching bugs), and I think the general feeling is that he probably does have a proof but it hasn't yet been thoroughly checked by others. (Who may be holding off because he's still changing his mind about the best way of writing it down.)