www.positivepromotions.com/Volunteers Volunteer Thank-You Gifts Under $5. Shop Online at Positive Promotions!
volunteers.aarp.org/ Register Free With Create The Good To Receive Volunteer Opportunities.
www.about.com/Become+A+Volunteer Search for Become A Volunteer. Find Expert Advice on About.com.
www.crossculturalsolutions.org/ From 1 Week To 1 Year Abroad. Volunteer and Travel the World!
www.zapmeta.com/Become+A+Volunteer Search Become A Volunteer Get Results from 6 Engines at Once
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