Collection of documents by the Agency for Healthcare Research and Quality.
http://www.ahrq.gov/clinic/epcix.htm

The Cochrane Library is a collection of six databases that contain different types of high-quality, independent evidence to inform healthcare decision-making, and a seventh database that provides information about Cochrane groups.
http://www.cochranelibrary.com/

DARE is a high quality database with structured abstracts of reviews published in the world wide literature, including otherwise difficultly accessible grey literature.
http://www.crd.york.ac.uk/crdweb/

This page provides specialized PubMed searches on healthcare quality and costs.
http://www.nlm.nih.gov/nichsr/hedges/search.html

This database contains evidence based medical material from more than 60 EBM sites.
http://www.tripdatabase.com/