Piklist makes it easy to show one or more fields, based on the value of another field, and so much more.
Using Piklist you can easily display your Menus as Radio, Checkboxes or a Select list (dropdowns). Easily include them in custom theme settings, or when creating posts. This simple tutorial will show you how.
Insert a subtitle filed to the Post screen
Chosen is a jQuery plugin that makes long, unwieldy select boxes much more user-friendly, and can easily be used with Piklist
Select2 is a jQuery replacement for select boxes, and can easily be used with Piklist