Is 'sola gratia' as a soteriology traceable in the period leading to the Protestant Reformation?

Protestants often consider the Roman Catholic church to have significantly distorted the gospel. Were there Christians prior to the Reformation who had essentially the same understanding of the doctrines of salvation (particularly _sola gratia_) as the later Reformers did? I'm interested in people between Augustine (approx. 400 AD) and Luther (1517 AD).