Mighty Form Styler for jQuery replaces you form select element with a html ul list so you can easily and completely style it with css. With some little magic it behaves just like a regular select element.
Kalypto lets you use a simple sprite or even just CSS to replace and style radio buttons and checkboxes.
jQuery plugin that monitors the form fields within the specified form or DOM container for changes, and will apply ‘dirty’ CSS class to the form and/or to DOM elements related to changed form fields (labels, spans, etc.). Provides several configuration options, public functions, and callbacks for customizing plugin behavior.
Replace RC Inputs lets you use CSS to style radio buttons and checkboxes.