Promethean Planet is 'the World's Largest Interactive Whiteboard Community'. 26,464 Resources are organized into categories, and sorted by resource type, age and subject. There is also a decent search engine, some paid for resources are included, and the site is UK based.
Smart Exchange is US based, but you can select England by changing the country. 33,522 Resources are held by subject, US grade and filetype, and some paid for resources are included.
