EasyBib.com

EasyBib no longer offers a free pro version for educational institutions, but you can still use the free (ad-supported) version of Easybib to create bibliographies in MLA format only, or purchase an individual subscription for additional features.

The same company that owns EasyBib also offers BibMe and Citation Machine. Both offer free citation creation services in several citation styles and for a number of different source types.

Looking for an ad-free alternative for creating bibliographies? Try ZoteroBib!