Where to find great ideas and arresting images (for free)
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."