The primary metric at the article level - a count of the number of times an article has been cited. There are three large, interdisciplinary databases that collect times cited:
Page views and downloads are considered 'emerging metrics', but are quickly gaining acceptance, particularly as an early indicator of impact for articles.
Institutional repositories, including our own repository, also tracks these metrics. See here for more details on our repository, or contact Chris Lewis, the digital repository coordinator, directly for more information.