There are two main types, the larger 'lima' type and the smaller Sieva type. The larger form, in cultivational history, was developed in Andean South America while the smaller developed in Central America and Mexico.

In the Carolinas, 'butterbean' refers to the smaller, Sieva type, pole-cultivated. In packaging, sometimes called 'baby'.
In other areas, 'butterbean' refers to a large, whitish variety, Phaseolus lunatus var. macrocarpus.

This is a source of confusion. The song is Carolina 'southern', so usually the small Sieva variety is meant, and it is a pole bean.

Both types are green when immature. In most cookbooks, lima bean means small and green while butterbean is the large yellow type.

There also are red, brown, black or mottled varieties.

Not sure what is meant when Europeans talk about the beans.

Seed source:
Lima Beans
I see that Carolina limas are sold out for 2010. The best!
Henderson cultivar also listed. Order early spring.