American Heart Association Professional Journals (Arteriosclerosis, Thrombosis, and Vascular Biology; Circulation; Circulation Research; Hypertension; Stroke)

BioMed Central (Biomedical research, peer-reviewed)

BioMed Central for handheld devices

Directory of Open Access Journals (DOAJ)

Directory of Open Access Repositories (OpenDoar)

Early Modern Literary Studies 

eScholarship Repository (peer-reviewed articles) (California Digital Library)

Harvard University Scholarly Repository (DASH) - Beta

HighWire Press (peer-reviewed journals)

Internet Library of Early Journals : A digital library of 18th and 19th Century journals

Journal of Visualized Experiments (video articles)

JournalJunkie (podcasts for medical practitioners)

NaturePreceedings

New Jour: Electronic Journals and Newsletters (Ann Okerson & James O'Donnell)

Online-Journals.org

Open Access Journals in Education

Popular Magazines on the Web

Proceedings of the National Academy of Sciences

Public Library of Science (peer reviewed)

PubMED and PubMed Tutorial
(over 15 million citations for biomedical articles from MEDLINE
and additional life science journals back to the 1950's)
(National Library of Medicine)

PubMed Central (Life Science Journals, peer-reviewed)

Registry of Open Access Repositories (ROAR)

RePEc (Research Papers in Economics)