HubMed

HubMed is an alternative, third-party interface to PubMed, the database of biomedical literature produced by the National Library of Medicine. Features include relevance-ranked search results, web feeds of query updates, direct citation export, tagging and graphical display of related articles.

There is a MediaWiki plugin for creating links to HubMed (though not for Wikipedia, see Wikipedia talk:PMID). HubMed also exports article citations in a format suitable for inclusion in Wikipedia articles.