I will talk about the sandpile group of finite graphs and directed graphs. I will state the Riemann-Roch theorem for graphs (due to Baker-Norine), say what can be known about the case of directed graphs, and how these things are connected to feedback arc sets. (This part is joint work with Blint Hujter.) I will also talk about a very nice connection between sandpile groups of ribbon graphs and planarity: By Chan-Church-Grochow and Baker-Wang, certain actions of the sandpile group of a ribbon graph on the spanning trees are canonical if and only if the ribbon structure is planar. With Tams Klmn and Seunghun Lee we gave a canonical definition for this action in the planar case.