The optimization of channel assignment in cellular mobile networks is an NP-complete combinatorial optimization problem. For any reasonable size network, only sub-optimal solutions can be obtained by heuristic algorithms. In this paper, six channel assignment heuristic algorithms are proposed and evaluated. They are the combinations of three channel assignment strategies and two cell ordering methods. What we found are (i) the node-color ordering of cells is a more efficient ordering method than the node-degree ordering; (ii) the frequency exhaustive strategy is more suitable for systems with highly non-uniformly distributed traffic, and the requirement exhaustive strategy is more suitable for systems with less non-uniformly distributed traffic; and (iii) the combined frequency and requirement exhaustive strategy with node-color re-ordering is the most efficient algorithm. The frequency spans obtained using the proposed algorithms are much lower than that reported in the literature, and in many cases are equal to the theoretical lower bounds.