I've taken the open souce ext_calendar component
(http://extensions.joomla.org/component/option,com_mtree/task,viewlink/li...)
and made some significant modifications to it. I cleaned things up
fairly considerably for creating search engine friendly urls, and I
ported the event administration to the back end. My goal is to turn
around and release this one to open source. I’ll see if I can’t
address some of the other user concerns and clean up the code more, but
this could be/should be a nice contribution back to the open source