What software or applications are available to help me with citing sources?

Zotero:

Zotero is a Firefox add-on that collects, manages, and cites research sources. It's easy to use and lives in your web browser where you do your work. See the Zotero Research Guide for more information.

EndNote:

Endnote is a software program which helps you manage and format your citations. See the Endnote Research Guide for more information.