MediaWiki+FCKeditor 

This combo works without any core file modifications:

MediaWiki 1.12.1
http://download.wikimedia.org/mediawiki/1.12/mediawiki-1.12.1.tar.gz

FCK Editor Nightly Build as of 10/16/08 7:30 AM PDT
http://mediawiki.fckeditor.net/nightly/svn/mediawiki_fckeditor_ext_N.tar.gz

This combo didn’t work – when clicking “edit” the screen turned white

svn checkout http://svn.wikimedia.org/svnroot/mediawiki/trunk/phase3
svn checkout http://svn.fckeditor.net/MediaWiki/trunk FCKeditor
wget http://www.fckeditor.net/nightly/FCKeditor_N.zip