EndNote Web - save your sources (web pages, scholarly articles, books), choose a citation style, select sources from your account, and create a works cited or references page in APA, MLA, Chicago or another citation style.
Zotero - a free, powerful extension for your Firefox web browser (you can download a connector for other browsers like Chrome or Safari) that enables you to save and organize your sources. You can select a subset of your sources and format them as a works cited or references list.
Important Note -- Citation generators are error-prone, so be sure to proofread! Double-check spelling, capitalization, and punctuation to be sure the official style (MLA, APA, etc.) required for your assignment is followed.
The Wittenberg Writing Center has compiled a long list of various online style guides.
Style manuals can be confusing (i.e. what does it mean to be "paginated by volume"?). For assistance, consult your instructor, the Writing Center, or a reference librarian.
Purdue Online Writing Lab (OWL) is a well-respected online resource for citation style assistance. If you click this link and scroll down, you will notice some buttons on the left-hand side that highlight guides for MLA, APA, and Chicago styles.
The Chicago Manual of Style, 17th Edition by 
MLA Handbook by 
Publication Manual of the American Psychological Association by