I'm using Nvivo on my windows work pc but am looking for something to use on my mac. I'm not sure how excited I am by HyperResearch (which I understand works on mac?), but I've only tried it out briefly in the past.
You might consider Tinderbox. No one, that I have seen has been able to push it enough to reach its limits. Check out some of the more advanced uses and the power it offers. Ted Goranson has done some interesting work recently. The developer, Mark Bernstein is very active in working with users: Tinderbox Forums.