Brusheezy.com is a site that hosts a ton of free brushes for Photoshop.  The brushes on that site have helped me to create all of the backgrounds and images for my site.  It is amazing how detailed some of the brushes are too.  The brushes are so detailed, in fact, you simply can choose the image you want and brush it onto a canvas, and create beautiful images.  And yes, Photoshop does allow you to rotate brushes and do all sorts of cool things.  If you don't believe in the power of brushes yet, just take a look at the pretty (somewhat pretty?) picture I created in under 1 minute using brushes.