Well, currently the big binary-centric Usenet app on the Mac is Unison, from Panic. It's a fairly young newsreader, and has a somewhat different paradigm than other newsreaders, but it works fairly well. The other options that I'm familiar with are Hogwasher, which is more traditional but rather crusty, and Thoth, which is a very good program (and what I use), but the developer killed it a year or so ago. If you can dig up a vaild licence somehwere, I highly recommend Thoth, though.
If it's a discussion-oriented reader you're looking for, there are several free choices in addition to the above (Thoth also handles discussions quite well, by the way), but I'm not as familiar with them.
IMO Thoth is not only the best newreader software prog for the mac, it is the best newsreader program for any platform. I have used many programs for the pc including agent and newzbin pro and Thoth has them beat hands down. If you can find a copy, I would highly recommend Thoth. It is so choice!!!!