Camino

Camino has a long history on Mac OS, and was on the scene before Firefox was a workable option. Even in its current state, I would argue that Camino is still the best Gecko browser on Mac OS. If you've used the Mac version of Firefox for any extended length of time, you'll realize that it's a memory behemoth and doesn't integrate well with the rest of the OS. I'm on a Mac mini with a limited amount of RAM, so speed and slimness are very important to me. (I was a windows user of Firefox so I used it for many months when I got my Mac, but have since switched to Camino.)

Supposedly Firefox 3.0 will bring some native cocoa features, but until then I'm sticking with Camino as my primary browser. The only real downside is less customizability through plugins (and themes if you're into that) although you can still tweak it internally with about:config and get some neat plugins at pimpmycamino.com.

Camino's major touted feature is that it uses Aqua buttons and controls and ignores what web designers specify using CSS. They achieved this and a small performance bump by using native Mac controls instead of XUL.

Tradeoff is that it "will never" support Firefox plugins (per their website) and it renders websites differently than IE, Firefox, Opera and Safari 3.

But hey, it stores website passwords in Keychain and was a nice proving ground for key developers who now work on more relevant projects.