We have studied the neutral-to-ionic transition in organic charge-transfer compounds in finite-size stacks. To describe these systems we use a model that includes (i) infinite intramolecular Coulomb repulsion, (ii) hybridization between nearest-neighbor molecules (t), and (iii) nearest-neighbor electron-hole attraction (G). Through a recently developed modified Lanczos method we obtain exact numerical results for the following physical quantities: (i) ground-state energy, (ii) occupation of acceptor molecules, (iii) a gap between the ground and first excited state, (iv) a gap between the ground and first triplet excited state, (v) charge-charge and spin-spin correlation functions, and (vi) neutral-ionic parameter phase diagram. The neutral-ionic phase transition is continuous for small G/t and abruptly discontinuous for large G/t, the crossover occurring around G/t\ensuremath{\sim}2. We also study the stability of both phases against dimerization and find that within the model the ionic phase is always unstable against this distortion, while the stability of the neutral phase depends on the value of the rigidity of the stack. We offer a strong-coupling argument that explains this result.