(please disregard this message if you already know this)
Someone mentioned old X-Wing vs TIE Fighter games as a good source of "clean" space-based sound F/X. Another good source, this time for land-based ones (anyone needing those landspeeder effects?) would be Jedi Outcast / Jedi Academy. Since they were made on Quake engine, the *.pk3 files can be simply unpacked using WinZIP/WinRAR to access "clean" (ie. no music in background etc.) sound F/X resources.