If you want to divide up your references at the end of a document so that they are grouped into certain categories, I have used the package multibib.
In the preamble, put the code
along with as many definitions as you like of the form
where xxx is an identifier and New Bibliography Name is the name of the new reference section.
Then to cite a reference and have it appear in the references New Bibliography Name you can use the command
\citexxx or \nocitexxx just as you would with \cite and \nocite.
Using this keeps all the existing citations using \cite and \nocite appearing in the bibliography at the end. Finally you have to specify where your BibTeX file is, and you may choose separate or different ones. I do this with the code