Ashley

Expanding Archives adds a widget that shows your old posts in an expandable/collapsible format. Each post is categorized under its year and month, so you can expand all the posts in a given month and year.
This plugin comes with very minimal CSS styling so you can easily customize it to match your design.
JavaScript is required. No IE support.

Expanding Archives

This plugin adds a new widget where you can view your old posts by expanding certain years and months.

robfelty

Create collapsible archives by year or month. Features include: link to archive pages, display of individual posts and support for custom post-types.
<h3>Demo</h3>
I use this plugin in my blog at http://blog.robfelty.com

Collapsing Archives

Very helpfull

This plugin uses Javascript to dynamically expand or collapse the set of months for each year and posts for each month in the archive listing of your  …

Expanding Archives vs Collapsing Archives