Association for Project Management (APM)
APM delivers education and develops qualifications, conducts research and provides resources. APM runs events, shares best practices and gives the project management community – individuals and businesses – the opportunity to connect and debate.
International Project Management Association
The International Project Management Association's goal is to identify, collect, document, certify, develop, freely share, and promote effective Project and Program Management practices.
The PM World Library (PMWL) is an educational resource for students of program and project management (P/PM) around the world. The PMWL contains educational articles, papers and stories about P/PM (see the PM World Collection), as well as information about books, journals, magazines and other websites. The PMWL is also intended to assist students with research critical to their studies. Students can register with the site to have access to its collection for two years.
From Usability.gov, this site provides a good overview of the fundamentals of project management with supplemental and related resources.
Project Management Institute (PMI)
PMI offers professional development resources, PMI standards and benchmarks, publications, and tools related to project management.
A one-stop shop for project management answers, helping get you "unstuck"—and confidently meet every new challenge that comes your way. Includes articles, on-demand webinars, blog posts, and more.