Google has relesed a search system which returns only accessible webpages: http://labs.google.com/accessible/
From the FAQ: Google defines accessible websites and pages as content
that the blind and visually challenged can use and consume using standard online technology, and we've worked with a number of organizations to determine which websites and pages meet those criteria. Our methods for identifying accessible pages and content are always evolving; Currently we take into account several factors, including a given page's simplicity, how much visual imagery it carries and whether or not it's primary purpose is immediately viable with keyboard navigation. http://labs.google.com/accessible/faq.html
