The interest in developing scholarly impact metrics is frequently justified by the need to objectively prioritize scarce resources and to better manage scholarly productivity. However, the study of scholarly communication in general, including scholarly impact metrics, has significant relevance to a number of other scientific domains such as computational social science, social network analysis, web science, and complex systems. In this presentation I will provide an overview of established scholarly impact metrics, grounding each in their respective scientific traditions and backgrounds. Changes in scholarly communication patterns, including the move to online environments and the increasing use of social media, have recently prompted a Cambrian explosion of new impact metrics derived from new data sources. These metrics may reflect previously unexplored facets of scholarly communication and impact, and may thus yield a more complete picture of scholarly communication. In my presentation I will provide an overview of these new metrics, and identify the opportunities as well as challenges that they present.