Before you start looking for volunteer opportunities, it is important to ask yourself a few questions: What issues do you want to support? How much time can you commit to a project? Do you want to volunteer once a week or once a month? Do you want to work for a national or local organization? See GiveSpot's list of 10 Tips for Volunteers for more advice.
After you've set your volunteering goals, visit VolunteerMatch. You can enter your zip code to find community service opportunities near you. The site's search options allow you to find nonprofit groups in metropolitan areas and beyond. Idealist.org is another great site with hundreds of volunteer opportunities.