"The Tree View Web Part provides users with the familiar Windows Desktop Explorer navigation, allowing them to manuever through any SharePoint list, document or picture library. Using folders in document libraries and grouping within the list views, users can organize any SharePoint list, library, discussion, wiki or site collection to display the hierarchy within. Users can group and display similar items into folders, such as high priority tasks, making it easier to navigate through large data sets. And now, in version 1.4, you can access a wide variety of data sources from Tree View via MashPoint."
Pricing (May 2009): USD 300 (per server)