CTAN update: bibexport
This is a shell script using BibTeX to extract .bib entries that are \cite'd in a document. It also permits to expand a BibTeX file, i.e. to develop abbreviations (except standard ones) and crossrefs.
This package is located at http://tug.ctan.org/tex-archive/biblio/bibtex/utils/bibexport . More information is at http://tug.ctan.org/pkg/bibexport (if the package is new it may take a day for that information to appear). We are supported by the TeX Users Group http://www.tug.org . Please join a users group; see http://www.tug.org/usergroups.html .
bibexport – Extract a BibTeX file based on a .aux file
A Bourne shell script that uses BibTeX to extract bibliography entries that are \cite'd in a document. It can also expand a BibTeX file, expanding the abbreviations (other than the built-in ones like month names) and following the cross-references.