Adventure-seekers might want to head on over to Opera, such the developers making an Alpha built of Opera 9.5 available for testing. I'd never advise using alpha software for production work, but if you are dying to try a new browser or just like to mess with new features, it's an interesting build.
They have done a good chunk of work on site compatibility, which is probably the most important piece of any underdog browser. I particularly like the summary text provided during a search. There are various fixes over Opera 9 as well, including some rendering issues.
As a browser, Opera has increased in popularity quite a bit since they made the very important decision to make their browser free a few years back. The 9.5 release is looking pretty spiffy, and worth a look if you are curious.