I believe you can accomplish what you are looking for using the List View Controls widget in the app store.
This will allow you to use a drop down list to filter the results within a list view instead of using the build in search functionality.
Not exactly a dropdown, but you could use the AutoComplete widget. Clicking on it lets you see attribute values and if you start typing, the list shortens. It only works like that if the attributes are distinct, otherwise you have to work on the display and display a difference, so that you do not end up with multiple entries that are exactly the same.