Saccharomyces is the main yeast used to produce beer/wine/bread. Saccharomyces cerevisiae is the main species of yeast used in the production of ale type beers, while Saccharomyces pastorianus is the species involved in the production of lager type beers. If you are looking for more information on yeast I highly recommend wasting a few hours reading through the information available over at Milk the Funk.