We all tag our WordPress posts sooner or later. You want to choose your tags wisely to keep your content organized and give your visitors an easier time exploring more topics on your site. There are various ways to display tags in your sidebar. These 3 plugins display WordPress tags as horizontal (percentage) bars:
Percentags Widget: lets you display tags as horizontal bars. You can include/exclude tags, change order, show total posts per tag, and modify colors.
Linear Tag Cloud: as the name suggests, this free plugin lists your tags as horizontal bars. You can change max number of tags, border color, and many other settings.
WP Category Tag Cloud: adds a configurable widget to WordPress, allowing you to list tags as horizontal bars, a flat list, price tags, and more. You can change the max number of terms displayed, colors, no-follow option, and other settings.
You could always write your own code to change how tags are displayed on your site. The above plugins simply save you time when you need to show tags as horizontal bars on your website.