I'm also working on a event based calendar.
<li>Smart navigation (AJAX)
<li>Adding Category with color
<li>Adding single-day events
<li>Adding repeating single-day events
<li>Adding multiple-days events
<li>Event details such as Title, Teaser, Text, Contact, Location, etc.
If you're interesseted in, I could post some screenshots.
My calendar should work like Google's but made with symfony and with nicer looking layout.
Greets from Austria,