Plugin Name: WYSIWYG Widgets
Plugin Description: Create easy rich text widgets without having to know HTML with WYSYWIG Widgets. This plugin adds a widget type which behaves exactly like the default WP Text Widget with just one difference; a rich text editor like you are used to from the post editor. Also you can use WP's media functions to upload and insert images and video into your widgets.
Plugin link: http://wordpress.org/extend/plugins/wysiwyg-widgets/
More info: WYSIWYG / Rich text widget editor
Got a great idea on how to improve this plugin or experience any bugs? Please, let me know!