volunteers.aarp.org/ Register Free With Create The Good To Receive Volunteer Opportunities.
www.cornerstoneondemand.com/ Reduce costs, improve quality, manage nonprofit. Learn More
www.uso.org/Donate Honor the Sacrifices of Our Wounded Warriors With a Donation to the USO
www.about.com/Become+A+Volunteer Become A Volunteer Search Now! Over 80 Million Visitors.
www.workandvolunteer.com/ Volunteer, Paid work, Gap Year. Make a difference - Apply today!
How I did it: i first googled to find the organizations that like, and then contacted them offering to become a volunteer and attended my first meeting at one of them, and now i'm officially their volunteer, yay :D
Lessons & tips: just do it, don't wait around too much, just google the organization you want and contact them right away, no need to be shy, go for it!
Resources: the internets, google