Opera, the revolutionary internet browser, hits version 9 today, with a host of new features - some better than others. I've been using Opera since version 6 and consider its speed and email client to be streets agead of the competition (not to mention tabbed browsing and mouse gestures).
With the addition of a BitTorrent client and Widgets, Opera should be able to make even more headway in the browser market. Their addition of a content-blocker, however, may lose them support of plenty of small-scale web publishers. We shall see.
First impressions are all good so far. If you're using a different browser, I recommend you check out Opera 9. It's free now (until recently it was ad-supported, with an option to pay for a full version without ads), and while it isn't everyone's favourite, it's definitely worth a good look.