My schedule is uncertain. My job or other circumstances make it difficult for me to commit on a regular basis. Furthermore, I thrive on variety. I'm interested in working with animals. These listings will give you an overview of the types of volunteer needs that exist, where they exist, and how to get in touch with the organizations.
Newspapers are a good source.
Also, if you come across an article about the activities of a local group that interests you, give them a call - there is a good chance they could use volunteer help. Your place of work is often an excellent source. Many employers encourage their employees to volunteer in their communities, sometimes on company time, and have already established relationships with local nonprofits. This is especially true of large companies such as Sun, Intel, and Apple to name only a few. Contact your company's human affairs or human resources office.