Couple other calendars to check out. I have not tried them out, yet. I really like the look and feel (demo) of Easy PHP Calendar, but like the idea of FREE with k5n.us WebCalendar. Out of all the searching I did about 4 months ago, these are the two php calendars that I really liked. Unfortunately the client I was creating a site with had no PHP support (gasp, I know!) so I never got a change to set either up.
Easy PHP Calendar - Pretty cheap license. $29 I believe.
WebCalendar - FREE