Go to advanced search, choose Creative Commons Commercial license and search away. The breadth is extraordinary, but what will amaze you is the quality. And the license is a generous gift from the photographer to you.
Another tip: when you are trying to brainstorm, Flickr is a great place to find connections between ideas that hadn’t occurred to you. Even if you don’t use the picture, the ideas are priceless. Do a search on lobster or clouds or crowds or quality and see what comes up.
Two last thoughts: be sure to check out the HDR images, and don’t forget to sort by "Most Interesting."