The DOAJ is a non-profit depository of open access journals that is both international and interdisciplinary in scope. The DOAJ only admits journals that practice some sort of quality control, whether it be peer review or an editorial process.
PubMed, a service of the National Library of Medicine, provides access to MEDLINE citations back to the mid-1960's and additional life science journals. It also includes links to many sites providing full text articles and other related resources.
This is a freely accessible site. Contents may change without warning.