Inspired by Vicsek's model, in this paper we propose two decentralized heading consensus algorithms for nonlinear multi-agent systems. The first algorithm, called WHCA, can be seen as a weighted Vicsek's model. The second algorithm, named LBHCA, is a leader-follower strategy based on the WHCA. It is proved that, under a well-known connectivity assumption, the algorithm WHCA can ensure almost global consensus of the headings, except for the situation where they are initially balanced. For the LBHCA, the global heading consensus is guaranteed under the same connectivity assumption. Simulation results are provided to justify the proposed algorithms.