BibMe is a great site for locating and generating bibliographic citations in MLA, APA and Chicago styles, which you can then download to your computer, or store on their server (if you sign up for a free account).
In their Help section, they provide detail as to where they get the bibligraphic information to generate the citations:
|Website:||Proprietary Web page parser|
|Journal:||CiteULike Academic Papers|
|Film:||Amazon DVD & VHS|
from BiblioTech Web