A systematic study of basis sets and many-body correlations for the treatment of-electronic excitations is presented. Particular emphasis is placed on the highly accurate treatment of transition energies within a computationally tractable scheme. All calculations have been performed using the Monte Carlo configuration interaction method and correlation-consistent basis sets augmented by diffuse functions constructed for the description of anions, and with the inclusion of additional Rydberg functions. The importance of a balanced description of the excited states and the ground state has been emphasized and the resulting electronic transitions have been compared with experimental values. We have found that the aug-cc-pVTZ basis set further augmented with Rydberg functions constitutes a good choice of basis set for which we report electronic excitations in excellent agreement with experiment.