We present an efficient method for computing the equifrequency surfaces (EFSs) and density of states of a photonic crystal. The method is based on repeatedly solving a small nonlinear eigenvalue problem formulated using the Dirichlet-to-Neumann map of the unit cell. A simple contouring algorithm is presented for sampling EFSs as well as computing group velocity vectors. We compare our method with several published results to demonstrate its efficiency and accuracy.