Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
BibBase - BibBase.org is an easy way to set up and maintain a scientific publications page.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
ProCite - ProCite is a tool for creating citations according to the standard defined by the users.
Citavi - Citavi is a program for Microsoft Windows that manages literary references and organizes organizational knowledge.
Papers by ReadCube - ReadCube Papers is a sumptuous reference manager helping out academic writers to get the most out when it comes to access and discovering more citations with multiple libraries or databases.