I'm a fervent user of the Opera Web browser. I've even paid for licences. It's fast, it's slick, but particularly I like the built-in e-mail client, "M2" (which also reads RSS/Atom blog feeds).
The big news with the release of Opera 8.5 is that Opera is now free! So if you haven't tried Opera before, I recommend giving it a try. I don't expect the Firefox users of the world to change over in great numbers, but if you are still using Internet Explorer, you may be seduced.