Just because a firm might have been considered "less ethical" or "not an ideal corporate citizen" by one listing or an organization, should not prevent that firm from wanting to change for the better.
So you should be careful before turning down an interview, since a firm might be looking for someone with your unique skill set & experience, to help lead that change!
Identifying Firms that Excel in Ethics:
World's Most Ethical Companies - annual compilation of the EthiSphere Institute and EthiSpehre Magazine - "helping corporate executives guide their enterprises toward gaining market share and creating sustainable competitive advantage through better business practices and corporate citizenship"
Identifying Firms that Excel with Corporate Responsibility:
Corporate Responsibility Magazine's 100 Best Corporate Citizens of 2015 - annual compilation by Corporate Responsibility Magazine since 2009 chronicling corporate transparency and accountability