If you've ever had to try and generate links to articles in PubMed, or URIs for use in RDF, you'll probably appreciate the NCBI Resource Locator which provides standardised URIs for NCBI resources.
Examples:
- http://view.ncbi.nlm.nih.gov/pubmed/12345
- Show the PubMed record with PMID 12345
- http://view.ncbi.nlm.nih.gov/pubmed/search/cancer
- Search PubMed for "cancer"