WordPress is the most popular blogging platform out there. WordPress has lots of great looking themes available for free. Serendipity is also a great blogging platform but it does not have the same range of excellent themes or templates that WordPress does.
If you are a Serendipity CMS user and would like to use a WordPress theme on your site I can help you. I have lots of experience working on original and ported Serendipity templates. For a reasonable fee, I can port or convert any WordPress theme to a Serendipity theme for use on your site. Please contact me if you need this service. Be sure to include links to the WordPress theme in question and, of course, your s9y powered website!