I had the WordPress NextGen GalleryView plugin installed, and decided to deactivate it. Doing that caused CSS & html to show up at the top of my product pages in my online shop (shopp plugin), and only on those pages. If I activated it again, the problem went away.
After a month of trying to resolve this on and off, and thinking I was just going to have to live with the plugin forever, I just now figured it out. The WP Facebook Open Graph Protocol plugin was causing it. When I deactivated it, the css & html that had been showing on my product pages was magically gone! I was using version 2.0.7