Well, there are a few I think that I should mention:
Chessmaster - This is a popular PC engine, but it's on Macintosh now too!
Hiarcs - Many chess players regard this engine as the strongest chess program for a Mac.
MacChess - Not as capable as the two engines above, but is has some use to it.
I hope these help! By the way, how are the resources going? Were you able to download them properly?
Chessmaster and MacChess are incapable and Hiarcs has a pretty monotonous interface.
Anything else?
Someone forgot to mention StockFish!!! 3200 elo, 25 moves ahead in less than a minute, and works on mac? Amazing!!! Thank you fishy!!!
i run shredder for linux on my ubuntu machine and it's REALLY nice. fast, smooth, strong, cool looking interface.
http://www.shredderchess.com/chess-program/shredder-12-mac.html
I use Stockfish 2.1.1 on my mac (just google "stockfish engine"), using the Shredder 12 and Exachess (http://www.exachess.com/) interfaces. It works great.
I am wanting something for the Mac as well. I am weighing the options of Parallels, VMWare, Bootcamp (all to run Fritz) or go Shredder 12. Does Shredder 12 have 3d boards? Also, someone mentioned the Hiracs engine. So Shredder lets you use other engines? or just the Hiracs engine?
I am sure any engine will be good for me based on my rating, but I would like the analysis to be as accurate as possible.
The Shredder 12 interface will let you use any Mac-compatible UCI engine, Stockfish being the strongest available (that I know of anyway).
I have Parallels, and Fritz was a major factor in my (mistaken) belief that I needed a Windows VM, but.. I dunno... I think I've been using Macs too long. The Fritz UI just seems convoluted and tragic to me now.
Anyway, here's a related post that goes into some detail on the Shredder interface. There is no "3D" option for the board display in Shredder. (And personally, I don't like the ones in Fritz, but to each his own. 
)
For years, I have used Rybka and absolutely loved it! Then, I worked some with Fritz, and thought it was great too! However, these only seem to work on a PC. On the Mac. all I can find is Shredder and Sigma. in my opinion, both of those are weak and do not have the capabilities of Fritz or Rybka. Also, their analysis is significantly inaccurate. Are there any good chess playing and analysis programs for Macintosh computers? Also, Fritz and Rybka both have great interfaces, so I don't really want something that looks like Shredder or Sigma either.
In addition, are there any forms of Chessbase that can be run on a mac? I keep searching for things, but have yet to find any. Please note that I am looking for a database, more so than a website.
Thanks,
Chessisgood