I'm not sure if Okteta is available for Mac as well, but it's a beautiful hex editor I use when on linux. WinHex is great on windows. I'll take a look if this might a good choice to use on my mac.
Okteta's beautiful from a user interface perspective, but like most hex editors it fails when trying to deal with large files. There are very few hex editors around that will open files that are larger than the amount of RAM that you have.
