As of this writing the Firefox 2 Beta 2 download page doesn't link to it but with this URL you can download Beta 2. I have been using Beta 1 ever since it was released and really came to like it (especially live, inline spell checking). So what does Beta 2 bring to the table you ask? A nicely refreshed look - new icons and tab styling. However, I do think that the updated look lacks contrast in the navigation toolbar.
Update: I forgot about the Windows users... Firefox 2 Beta 2 download link.