Here is a quick reference guide for finding volunteer opportunities:
General
Create the Good - www. createthegood.org
DoSomething.org: www.dosomething.org
TeenLife; www.teenlife.com/category/volunteer
United We Serve: www.serve.gov
United Way: www.unitedway.org/take-action/volunteer
Vounteer.gov: www.volunteer.gov
VolunteerMatch.org: www.volunteermatch.org
Mentoring
Best Buddies: www.bestbuddies.org/volunteer
Big Brothers, Big Sisters: www.bbbs.org
Mentor Up: www.mentorup.com
National Mentoring Partnership: www.mentoring.org
AID
Children's Miracle Network Hospitals: http://childrensmiraclenetworkhospitals.org
The Red Cross: www.redcross.org/support
Habitat for Humanity: www.habitat.org/youthprograms
Animal Welfare
PAWS: www.paws.org/kids/volunteer
The Humane Society of the United States: www.humanesociety.org/community/volunteers
Citizen Science
EPA Volunteer Monitoring Program: http://water.epa.gov/type/rsl/datait/waters/georef/epasvmp.cfm
Scientific American: www. sceintificamerican.com/citizen-science
Mitten Crab Watch: http://mittencrab.nisbase.org
The Great Sunflower Project: www.greatsunflower.org
The Lost Ladybug Project: www.lostladybug.org
General
Create the Good - www. createthegood.org
DoSomething.org: www.dosomething.org
TeenLife; www.teenlife.com/category/volunteer
United We Serve: www.serve.gov
United Way: www.unitedway.org/take-action/volunteer
Vounteer.gov: www.volunteer.gov
VolunteerMatch.org: www.volunteermatch.org
Mentoring
Best Buddies: www.bestbuddies.org/volunteer
Big Brothers, Big Sisters: www.bbbs.org
Mentor Up: www.mentorup.com
National Mentoring Partnership: www.mentoring.org
AID
Children's Miracle Network Hospitals: http://childrensmiraclenetworkhospitals.org
The Red Cross: www.redcross.org/support
Habitat for Humanity: www.habitat.org/youthprograms
Animal Welfare
PAWS: www.paws.org/kids/volunteer
The Humane Society of the United States: www.humanesociety.org/community/volunteers
Citizen Science
EPA Volunteer Monitoring Program: http://water.epa.gov/type/rsl/datait/waters/georef/epasvmp.cfm
Scientific American: www. sceintificamerican.com/citizen-science
Mitten Crab Watch: http://mittencrab.nisbase.org
The Great Sunflower Project: www.greatsunflower.org
The Lost Ladybug Project: www.lostladybug.org