Terence Eden

If you have a long and rich history of blog posts, you’ll want this plugin. It automatically produces a calendar showing how many posts per month you’ve made.

Edent's Archive Calendar Widget

A sidebar widget to display all of your posts in calendar form. Suitable for sites with very large archives.

mva7

This calendar comes as a widget that shows your upcoming events. If you want you can automatically import the holidays from http://www.theholidaycalendar.com.
Two views are available: calendar view and list view.
If you choose to import the holidays they are fetched from a webservice. This happens asynchronous so your website will not get slow.
For more information about the webservice visit: http://www.mva7.nl/the-holiday-calendar-webservice-manual.html

The Holiday Calendar

An awesome calendar plugin that just works! Shows the upcoming holidays and/or your own events.

Edent's Archive Calendar Widget vs The Holiday Calendar