Really quality wordpress themes at http://www.motiontheme.com i purchased one called News Friendly theme and it is really great quality work. If you are looking for premium and custom made wordpress themes with premiumd design i suggest to check http://www.motiontheme.com
Besides the sources suggested by other fellow members, there is another one which hosts some premium WordPress themes and allow users to download them for free.
You can just give it a try at http://nulledstylez.com/category/wordpress_themes/premium/. Also you can search online on Google for some more.