Biology Browser – Access to evaluated and curated digital resources
ipi2 Science and Technology – United States service. Features a searchable subject categorized directory of authoritatve websites; links to online texts, newspapers, magazines, podcasts etc. Search by subject
National Science Digital Library (NSDL) – Search by subject and resource format
National Science Foundation – Search classroom resources
PubMed Central – A free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health’s National Library of Medicine (NIH/NLM).
Wellcome Trust – Search under ‘Electronic Resources’