  We introduce a family of Jastrow pair product states for quasi
one-dimensional spin systems. Depending on a parameter they interpolate between
the resonating valence bond ground state of the Haldane-Shastry model
describing a spin liquid and the (dimerized) valence bond solid ground states
of the Majumdar-Ghosh spin chain. These states are found to form an excellent
basis for variational studies of Heisenberg chains with next nearest neighbour
interaction and bond alternation as realized in the spin-Peierls system
CuGeO_3.
