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.