Google Scholar Citation
Google Scholar gets the information (title, authors, journal name, date,...) directly from google scholar indexed journals. It produces the different styles from that information. Usually this works quite well, however, sometimes things go wrong so it's always good to check if everything is correct.

I also recommend using a citation manager like endnote or mendeley, that way you can download citation styles directly from the source/journals, manipulate them, easily change styles and correct errors.