I have spent a little time developing a widgetWindow component for the Flex API that gives you the exact look and feel of widgets that are in the Flex Viewer, but are really just custom extended TitleWindow components. The widgetWindow minimizes and maximizes just like the viewer widgets and are draggable and resizable.
There is still a SIGNIFICANT amount of programming skill need to use this, but it is a good starting point and example.
All the code you need and an example of how I took my Enhanced Search Widget for Flex Viewer and migrated it to work non Flex Viewer is available here:
