Almost any shrub that blooms in the shade will bloom more profusely is the shade is not too dense. However, if nandina grows well in the location, there are some shrubs that should work for you. Most viburnums tolerate a fair amount of shade and drought. Aronia (chokeberry) and panicled hydrangea also will bloom in the shade, but they prefer moist soilt conditions. Yellow wax bells (Kirengeshoma palmata) is a shrubby perennial that could do well here, too.