It may strike you as odd that an economist is advocating volunteer work. After all, aren't we the ones that always assume that people are motivated only by greed? Well, we don't either assume it, generally, or believe it to be a true and accurate description of human nature. But for many purposes it is useful to abstract away from the complexity of the real world to get a handle on a small part of that world. So economists often assume that individuals derive satisfaction or happiness only from the consumption of goods and services, and that looks like greed to the uninformed.
Anyway...Here are some volunteer organizations I find especially worthwhile.
If you are handy at construction, demolition or just willing to work up a sweat helping someone get a decent place to live then join UMBC Habitat for Humanity or contact Sandtown Habitat for Humanity to volunteer.
If racial justice is important to you, and you live in the Baltimore metropolitan area, consider joining a study circle through the "Call to Community: an Honest, Conversation about Race, Reconciliation, and Responsibilty". This program is sponsored by Interfaith Action for Racial Justice which can be reached by phone at 410-889-8333 or via email at iarj@mail.bcpl.lib.md.us.