Essential information is the Drupal version. Did you try: http://drupal.org/project/themes ? Also, themes as Zen are easy to customize and have enough documentation for beginners so you can create your own unique design.
I agree with dennisb. Use the Zen theme. It has great documentation and its actively maintained. Here is a great video introduction on the Zen theme. Search YouTube for "Drupal 7: Basic Theming with Zen and CSS" Here is another video that goes in a little more depth. Search YouTube for "Drupal 7: Theming Fields and Nodes with Templates" There is also a module called "Zenophile" that easy creates the sub themes for Zen, but do not use this module on a live site because of the file permissions needed.
Danland is one of my favorite drupal theme. It is free. Danland is clean, simple, elegant, and beautiful theme for Drupal 6.x and Drupal 7.x. This theme includes an image slideshow or photo slideshow feature on standard installation, Danland also include one subtheme without slideshow feature. http://drupal.org/project/danland
You can search it on Google or you can download and update it from official website of drupal. Sites in drupal are more good and reliable.
Themeforest has some very nice Drupal themes: http://themeforest.net/search?utf8=%E2%9C%93&term=Drupal