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.