There are many free Drupal themes that will assist you in getting just the right message and/or opportunities for your visitors and other readers to sign up and/or buy from you! Some of the best are:

The free Drupal Poker Theme: The best in the free area when you want to start a gambling website. It is made in the very lush green that says money and, of course, implies the felt that is the mainstay of most gambling tables. The template has a three-column design with a nice poker header and comes complete with drop down menu functions.

The Real Estate Drupal Theme:  It comes with a customizable header, very eye-catching design and is the perfect look for starting a Real Estate web site that will have people wanting to come, look, and stay for a while!

A very clean and simple design for a blog that has as its main feature, simplicity is the Pixelgreen. It has left side / right side column swapping, support for all operating systems and with built in comment styling, and SEO optimization features.