There are numerous plants that work well in combination with rhododendrons. You can get some ideas by looking at our planting plans that contain rhododendrons. Go to http://www.bhg.com/gardening/plans/ to check them out. You could also go to the advanced search option of our plant encyclopdia and search for plants that grow well in your Zone in partial shade. You'll find that link at http://www.bhg.com/gardening/plant-dictionary/advanced-search/.