as seen at freshmeat, and at SIXPACK site: "SIXPACK is a free BibTeX and Reference Manager designed to edit, convert and manage reference files, search and sort bibliographies, import and export many different bibliography types. Sixpack uses the excelent perl package bp by Dana Jacobson to covert between formats." and it reads/writes bibtex, refer, endnote, tip, procite, rfc1807, and plain text along with one-way for several others. written in perl/tk... looks real good.
as seen on gnome-list, what's new includes "multiple documents interface, with copy/paste and drag'n'drop; multiple selections (useful with LyX citation for example); all the supported formats (bibtex, medline, ovid, refer) can now be read and written; better date handling; bug fixes." for more see the pybliographer download page at gnome.org. if you haven't tried this yet give it a shot; i might finally get rid of endnote + msword (and there was much rejoicing). :)