OK, so ZSNES has always had support for Mac OS X, but I've added a few changes that make it a "true" Mac OS X app. This is mostly adding configuration data to the ".app" bundle NextSTEP - I mean, Mac OS X - uses.
Sadly it did involve some mucking with the ZSNES code itself - mainly to change the main method (since I'm not using SDL's normal Mac OS X startup) but also due to a few other issues (such as memset/memcpy being too smart for their own good and bombing if they thought they'd overflow the buffer they're writing to).
I also had to add some code to ignore the "-psn_0_x" argument that Mac OS X passes to applications launched from Finder. (What's it for? No clue. And since PSN means "PlayStation Network" to Google, I haven't had any luck finding out.)
Next up there's some additional glue code to intercept the "open document" message Mac OS X sends. Unlike most other OSes, double clicking on a file registered to an application doesn't just invoke the application with the file as an argument - it sends a special message to the application instead. There's some other UI-related code changes (such as making the buttons in the About dialog work under Mac OS X).
In short, this isn't just "./configure && make && make install", there is some actual new stuff here.
Some screenshots:


I haven't really tested this to make sure it works, but if anyone wants to try it: ZSNES 1.51-3.dmg
My SVN repository is also online for the code: http://svn.xenoveritas.org/zsnes/trunk
This repository includes an embedded copy of SDL, which is missing any code not related to the Mac OS X port. Likewise, the Windows/DOS specific code for ZSNES is missing in that repository.