I was looking for a customizable theme for a friend, and after hunting high and low, came across this huge list of themes at http://www.bestwpthemes.com. The author has categorized them into one-column, two-column, three column, magazine style, photo-gallery, specialized themes (for special purpose sites), paid themes and “resources”. I find the last one a bit confusing, it should in my opinion be called “theme generators”. A thumbnail of each theme would also help. Nevertheless, it is an excellent compilation of themes, and the author apparently takes pains to update the list regularly. Do look it up.

Smashing Magazine too regularly publishes a list of excellent wordpress themes to inspire you.