You can download one of the many community-created themes from the drupal.org site and customize it as much as you want. In fact, some themes have been specifically designed to be used as frameworks for customization or to be extended with sub-themes.
You must install and configure each theme individually on your machine. You should only use a theme that is available for your Drupal version.
The following list is just a sample of some useful themes. More themes are being constantly added to the site. You can find the latest themes in the Drupal contributed themes section.
For information on where to install a theme, see the installing themes page.
NOTE: Not all contributed themes are listed here, and some of these docs have not been updated to the most current theme version. Please help by contributing documentation for those that are not listed here and by updating those that are. When possible, work with the theme contributor to ensure accuracy.