Certification Courses for Project Managers
Useful Project Management Resources
Project-Management: Good reference site for Project Managers
A Girl's Guide to Project Management: Blog run by Elizabeth, a career PM. Has tons of useful articles.
Wrike Blog: Has great articles on Project Management from Wrike team
Camel Blog on Project Management: Articles, book reviews, Q&As, career advice on Project Management
Mountain Goat Blog on Agile and Scrum: This is a very informational blog run by co-founder of Scrum Alliance and Agile Alliance.
PMI's Project Management Journal: Most of its articles are for PMI members. A great resource.
International Journal of Project Management: Paid subscription. Published by Association for Project Management (APM) and the International Project Management Association (IPMA)
Journal of Modern Project Management: Quad-monthly basis scientific journal of studies focusing on the area of project management