You can also reheat beans in pans in the oven, stirring occasionally, once they start getting hot.
Remember that it is important to cool beans (or any other hot food) quickly too. A pot of beans can hold heat for a long time. Not only is this not good food safety-wise, it can lead to souring of the pot. To cool more quickly, transfer the beans into smaller containers, put them on racks or otherwise prop them up so there is air circulation underneath and stir periodically to release the heat that can build up in beans (and thick soups, etc.). Alternatively, place the bean pot in the sink and surround with cold water and lots of ice. Stir periodically, replacing the ice as it melts and draining excess water as needed so it doesn't overflow the pot. (If doing very large pots of beans, separate into two or three pots for cooling and stick in the bathtub with water and ice. Remember to stir periodically to release heat.)