  In 2D conformal quantum field theory, we continue a systematic study of
W-algebras with two and three generators and their highest weight
representations focussing mainly on rational models. We review the known facts
about rational models of W(2,\delta)-algebras. Our new rational models of
W-algebras with two generators all belong to one of the known series. The
majority of W-algebras with three generators -including the new ones
constructed in this letter- can be explained as subalgebras or truncations of
Casimir algebras. Nonetheless, for one solution of W(2,4,6) we reveal some
features that do not fit into the pattern of Casimir algebras or orbifolds
thereof. This shows that there are more W-algebras than those predicted from
Casimir algebras (or Toda field theories). However, most of the known rational
conformal field theories belong to the minimal series of some Casimir algebra.
