Lightweight, easy to use and no dependencies.
Labelauty is a nice and lightweight jQuery plugin that gives beauty to checkboxes and radio buttons and allows custom labels for each status of (un)checked inputs.
Tagator is a jQuery-based replacement for input boxes, making them tagging boxes. It supports searching, and affects the original input box directly, which is used as a comma serparated data container.
jQuery Custom Form plugin that allows you to play with input type(checkbox and radio) design, with disabled action and custom SELECT.
Fancyform is a jQuery plugin that offers a nice and elegant way to transform your HTML elements into custom styled elements. It's easy to implement and customize.
The elements you can style are input:radio,input:checkbox, select and textarea