PubMed Central, the National Library of Medicine's free online archive of biomedical literature, celebrated its 10 year anniversary this past February. (And I missed it!)
PubMed Central started back in 2000 with only two journals; now there are over 600 journals freely available to researchers and the public. The NLM Technical Bulletin gives a short overview of its history.
Lately, PubMed Central has been growing more quickly due to the NLM Public Access Policy. You'll see many links from PubMed to full text articles in PubMed Central. Just think, if you ever work on an NLM grant, your article will be available in PubMedCentral for all to read!