The default WordPress Archives widget is a simple way to let users access your posts by year and month. However, if you’ve been writing for a few years, you might find this list getting a bit big for your sidebar widget area. Enter the jQuery Archive List Widget by Miguel Useche. After installing you’ll find the Archive List widget available at AppearanceWidgets, insert it into your Sidebar or alternative widget area, and you’re done, it works straight out of the box. Once inserted open the widget to customize the display options.
The result is an archives list, much like the standard widget, however now each year is compressed into a single line, once clicked the month links are exposed below.