http://wf.codeplex.com/ contains a plethora of infrastructure code and new activities for extending Workflow Foundation 4. These are also available as Nuget packages.
These include:
- Activity Extensions
- Security Activity Pack
- ADO.NET Activity Pack
- Azure Activity Pack
- Activity Unit Testing Framework
view my PowerPoint presentation on these and more here: http://www.slideshare.net/joshuareuben9/workflow-foundation-activity-packs-extensions-and-unit-testing