I’ve created a new project for Behaviors on CodePlex, the WPF Behavior Library. A behavior is basically just a set of attached properties and functionality you can attach to a visual element. By attaching the behavior to the bit of UI you give it the additional functionality.
The first behavior I’ve included is Drag & Drop. There are a few drag and drop behaviors out there right now but they all require a lot of modification to use in other applications. Most of them only work for a subset of the UI elements that inherit from ItemsControl (mostly the ones that have their own ItemsContainers), some can’t move items between windows, and some don’t allow you to change logic behind moving items. In short none were general purpose enough to just grab a dll and use the behavior.
So take a look at the WPF Behavior Library, give feedback, report bugs, suggest new behaviors and features, or contribute.