I teach basic Maths in the UK. A lot of us use

http://www.skillsworkshop.org/

You upload a worksheet or game (granular level, something like 10 or 20 minutes of class time) and the moderator checks it over and classifies it by the level/type. Then it appears as a pdf.

If you upload a lot, you can ask for access to the editable versions of other files. This sort of addresses the 'free ride' problem.

At present, the site is a lot of work for one teacher, but she is recruiting moderators to spread the QA load.

A more commercial example is that run by the Times Educational Supplement (TES, trade paper of teachers over here).

http://www.tes.co.uk/teaching-resources/

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