  We present first results from the Southern Cosmology Survey, a new
multiwavelength survey of the southern sky coordinated with the Atacama
Cosmology Telescope (ACT), a recently commissioned ground-based mm-band Cosmic
Microwave Background experiment. This article presents a full analysis of
archival optical multi-band imaging data covering an 8 square degree region
near right ascension 23 hours and declination -55 degrees, obtained by the
Blanco 4-m telescope and Mosaic-II camera in late 2005. We describe the
pipeline we have developed to process this large data volume, obtain accurate
photometric redshifts, and detect optical clusters. Our cluster finding process
uses the combination of a matched spatial filter, photometric redshift
probability distributions and richness estimation. We present photometric
redshifts, richness estimates, luminosities, and masses for 8 new
optically-selected clusters with mass greater than $3\times10^{14}M_{\sun}$ at
redshifts out to 0.7. We also present estimates for the expected
Sunyaev-Zel'dovich effect (SZE) signal from these clusters as specific
predictions for upcoming observations by ACT, the South Pole Telescope and
Atacama Pathfinder Experiment.
