SDSS-II Supernova Survey Data
While SDSS-III does not have a dedicated supernova observing program, supernova data from a previous incarnation of SDSS (SDSS-II) are still available. SDSS-II, which ran from 2005 to 2008, included a Supernova Survey, described in detail at the Supernova Survey section of the original SDSS website.
Data available from that site include a list of spectroscopically confirmed supernovae, supernova lightcurves, and a link to a supernova analysis package that SDSS-II used. The raw images taken by the Sloan Foundation Telescope as part of the SDSS Supernova Survey are available as JPG preview images from the Stripe 82 Catalog Archive Server (CAS) Get Images tool, and as FITS files from the SDSS Data Archive Server. If you are specifically interested in the Stripe 82 Coadded files, those are available here.