aposai

Display your archives in collapsible mode using ajax and jQuery.
Each subnode is loaded via ajax as per user request, so not whole archive is loaded each time your archives page is displayed. If you have performance problems or server issues with other archive plugins, try this one and enjoy.
It also displays the post count for each year and for each month and the comment count for each post. And uses your current wordpress date_format to format the dates.

Ajax Archives

Display your archives in collapsible mode using ajax and jQuery.

Heath Harrelson

This widget is designed to be a more compact alternative to the default archives widget supplied with WordPress. If you’ve been blogging regularly for several years, the archive list produced by the default widget grows to be quite long. If you use Flexo Archives instead, the list will be displayed as a much smaller list of years. When you click a year, it expands to show the months of that year when you posted. By default the expansion is animated.
A standalone version that simply prints the HTML for the archive lists and attaches the JavaScript to normal pages is now provided for users who cannot use the widget.
I am currently seeking translations of the plugin. If you would like to help by translating the plugin into your language, <a href="https://wordpress.org/tags/flexo-archives-widget" rel="ugc">please post to the support forum</a>.
Thanks to Dylan van der Heij for providing a Dutch translation.

Flexo Archives

Displays your archives as a compact list of years that expands when clicked.

Ajax Archives vs Flexo Archives