BibTeX is the bibliography format if you are working with LaTeX. Emacs has a very nice mode for editing BibTeX files, in particular if you add

(setq bibtex-maintain-sorted-entries 1)
(setq bibtex-clean-entry-zap-empty-opts nil)

to your .emacs file. However, sometimes it can be easier to have a specialized GUI. People suggested

• http://www.pybliographer.org/
• http://jabref.sourceforge.net/

Both tools are said to be easy to use and to have many options for importing (e.g. directly from electronic data bases such as INSPEC) or exporting (e.g. to endnote). However, I never had time to test them …