Boston University's Community Service Center
Boston University has an extensive Community Service Center that provides services to students of BU (and by extension, BUA). They are located on the fourth floor of the George Sherman Union (GSU). If you need help designing a project or finding good organizations with which to work, they are an invaluable resource.

Volunteer Match
Volunteer Solution
These two links go to clearinghouses which pull together volunteer opportunities from many organizations. They may provide you with everything you're looking for, or they may just give you the good ideas you need to get started.

National Service Initiative
While as yet merely a linking site, the serve.gov site does provide links to local organizations participating in National Days of Service.