open source content management systems?

hi all does anyone have any recommendations for good open source content management systems for websites? - preferably, written in php... i have about a 50000 page site running on a freebsd/apache server. it gets a fair number of hits a day. right now, the great majority of my pages are statically generated by my 30+ ftp users. there is no consistency of layout between sections of the site. i wanted to investigate open source content management systems in order to make our pages easier to create and update (preferably so i can do away with the majority of my ftp accounts and have my users create and update pages from a webbrowser), and maintain a consistent layout scheme across the site. i'd also be into investigating commercial cms's, although i'd like to stick with open source if possible... thanks redmond