Ab initio results are reported for the excess-electron systems M(2)X, M(3)X(2), M(14)X(13), and M(18)X(17). In addition to self-consistent-held (SCF) calculations, electron correlation effects are taken into account for the smaller clusters by second-order Moller-Plesset perturbation theory (MP2) and the single- and double-excitation coupled cluster method with a perturbational estimate of triple excitations CCSD(T). For the smaller systems stationary geometries are characterized as local minima by SCF and MP2 force field calculations. The excess electron is either localized in an anion defect location or at a weakly bound alkali atom in all cases.