Google Chrome for OS X
Here's a short & sweet review of the Gold version of Chrome for OS X.
Pros: Lightning fast page-rendering. I mean, seriously. It's Hammer Time fast -- you can't touch this.
Cons: If you like Safari, you'll hate the way Chrome handles tabs and bookmarks.
The jury is still out on whether Chrome's rendering is fast enough to make up for what to me is a clumsy interface. I always have enough windows and tabs open (usually a dozen windows, each with multiple tabs) that waiting for a page to render is no big deal. But speedy navigation through all those pages is vital.