KBibTeX
KBibTeX is a bibliography editor for KDE and is most often used in conjunction with Kile. KBibTeX's primary file format is BibTeX as known from LaTeX, but other formats such as RIS or EndNote can be imported and exported.
Currently, there is a stable version for KDE3, for which most Linux distributions include packages for easy installation. A version for KDE4 is under development, but not yet stable enough for regular use.