I just stumbled across two new and interesting Mac browsers. Shiira is a web browser based on Web Kit, like Safari. It behaves very much like Safari but has lots of additional and interesting features. For example, the View Source window also shows you the HTTP Header request and response. It supports a sidebar, complete with extras like a page holder and RSS viewer. A very interesting feature: Hit F8 to see all of your browser tabs, Expos? style!
Check out also Shiira mini, a version of Shiira for the dashboard. It is small, fast, and even supports Flash. You can have multiple browsers on your dashboard, and set different home pages for each. Pages are shrunk down and difficult to read, but they do fit into the dashboard layout well enough.
Both of these browsers are very interesting. They are definitely not ready for prime time, but they do show a lot of promise and some neat new ideas.