i really like
Stainless. It is still in beta and the developers at mesadynamics are working fast toward a 1.0 release. It's speed is amazing and is much faster than safari or firefox. It's main feature is parallel sessions. Each tab runs as a separate process, making the browser run faster as a whole, and also making it a very light program. This makes it possible to log into the same website with different credentials in each separate tab.
Another cool features is the bookmark shelf. This is a little bar at the left side of the screen that allows you to drag website favicons from open tabs onto it and it saves them as bookmarks. This acts like a dock within the browser and makes getting to bookmarks very quick and easy. If you need the screen real-estate it has an auto-hide feature just like the dock.
It is still in development and the next big thing they are working toward is session restore, as well as keychain integration for passwords. I encourage you to try it because I really like it. It is not a production ready browser but is still very stable. It lacks main features that a browser would have so I would just use it as a test browser.
I actually use it as my main browser but that is because I like it enough to deal with the lack of all features.