Professional societies: 

  • Project Management Institute. Select Knowledge Center to view sample publications like PM Network
  • International Project Management Association. Select Research and RMB publications to access a lot of free information
  • . Association for Project Management in the UK
  • . American Society for the Advancement of Project Management
  • . Australian Institute of Project Management

Sites with articles related to project management (sites above also have articles):

Here’s an interesting article about Gantt charts from

Link with more info on quantitative risk analysis techniques