I like EventCalendar3 (EC3) because you can subscribe to the posed calendar events from iCal (OSX), Sunbird or Google calendar. It’s now under the care of Alex Tingle and you’ll find it here: http://wpcal.firetree.net.
Starting from WordPress 2.5 EC3 wouldn’t work properly. There are patched files to make it good again. The issue and a downloaded fix is documented here: http://penguin.firetree.net/pipermail/eventcalendar/2008-September/003289.html