MedlinePlus is a free, comprehensive, authoritative, up-to-date health information website from the National Library of Medicine.
The National Library of Medicine produces and maintains databases ranging over all kinds of medical topics. A listing of the databases can be found at this link: http://wwwcf2.nlm.nih.gov/nlm_eresources/eresources/search_database.cfm
Some NLM databases that may be especially useful to nurses include: