EasyBib is a great online resources that helps students cite their sources for FREE!  I have used EasyBib a lot and really love that it is easy to use.  EasyBib has MLA, APA, and Chicago style citations available.  If your students are citing sources I encourage you to introduce EasyBib to them.  Check out the Student Resources section for more writing tips.  You can also download the EasyBib iOS app and Android app.