If you want direct access to all your assets, with previews and filtering at all times, this plugin may be of use for you. It adds a bottom panel that lists, grouped and filtered, all of your imported resources. You can use drag-n-drop from the panel to add resources to the scene or to the node properties in the Inspector.
It's a bit slow at the moment, but this can be improved in future versions.
This project is provided under MIT License.