Yes, and one of them would be used in conjunction with a revocable living trust. If you were to create one of these trusts, you may have some assets in your direct personal possession at the time of your passing. A pour over will would allow these assets to be absorbed by the trust after you are gone.
Another will that should be part of every estate plan is a living will. In this document, you state your preferences with regard to the utilization of artificial life-support measures.