ONS has just published the 2011 Census Geography products at http://www.ons.gov.uk/censusgeography.
These products, detailed in the 2011 Census Geography Prospectus, include boundaries of the modified output areas (OAs) and super output areas (SOAs). They have been made available ahead of the 2011 Census second release estimates, and can be used under Open Government Licence.
OAs and SOAs are the core statistical geography from which estimates for all higher geographies are produced, including all 2011 Census statistical releases, in line with the Geography Policy for National Statistics. They are therefore not only a key 2011 Census delivery, but also one that provides the geographical base that is used to inform policy, planning and resource allocation across the public and private sectors.