Elderberries generally require two varieties for fruit set (pollination) purposes.
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Bob Gordon has sweeter, larger berries on 8-foot-tall bending canes that are ready to harvest in July. Zones 4-8. Optimal pollination from any variety.
 
Wyldewoo has the large cymes of this cultivar make up for it having the smallest berries. It offers 5-8-foot-tall bending canes with fruits ready to harvest in August. Zones 3-8. Optimal pollination: Ranch.
 
Adams is a highly productive, semi-fertile and vigorous cultivar that produces large clusters 5 inches in diameter on 8-foot-tall upright canes. Harvest in mid-August. Zones 4-9. Optimal pollination: Johns.
 
John is the highest yielding variety that is highly adaptable to any soil type when irrigated. It produces on 10-foot-tall upright canes. Harvest in mid-August. Hardiness zones 3-8. Optimal pollination: Wild.
 
Ranch is the best choice for extreme climates, this variety has 5-foot-tall upright canes that are easily harvested and highly productive, even in non-fertile soils. Harvest in August. Hardiness Zones 3-8. Optimal pollination: Wyldewood.
 
Wild is considered as the best all-around pollinator due to its long blooming period. It is also extremely adaptable. However, the cymes lack density and the berries are small on its 10-foot-tall bending canes. Harvest from August to September. Zones 3-8.

Disclaimer: berries should be ripe and cooked before eaten as some people have sensitivity to the alkaloids present. They are always poisonous when unripe.