Sodium clusters (Na-x, x less than or equal to 100) were collided with A = TCNQ, C-84, C-60, Br-2, or SF6 at near-thermal energies under crossed beam conditions. Efficient single collisional ionization was observed for all A. Resulting cations and anions were studied by mass spectroscopy. Resonant electron transfer followed by charge separation to yield parent cluster cation (Na-x(+)*) and anion (A(-)*) pairs is an important channel-given sufficient center of mass kinetic energy. It is the only charging process observed for the fullerenes and TCNQ. For Br-2 and SF6, electron transfer can give rise to either charge separation or bond reanangement/chemi-ionization. We discuss factors influencing the energetics, inelasticity, and probability of electron transfer/ion-pair formation in these systems.