A helpful article from Gus Garmel, Senior Editor of The Permanente Journal:
Garmel G. Reviewing Manuscripts for Biomedical Journals. Perm J 2010 Spring;14(1):32-40.
Valuable resources for reviewers from the British Medical Journal:
Guidance for peer reviewers from the Equator Network:
Guidance for reviewers and editors, with a specific focus on ethics, from the Committee on Publication Ethics (COPE):
Another article about peer review:
Cummings P, Rivara FP. Reviewing Manuscripts for Archives of Pediatrics & Adolescent Medicine. Arch Pediatr Adolesc Med 2002 Jan;156(1):11-3. DOI: http://dx.doi.org/10.1001/archpedi.156.1.11.