AJAX Upload is a free script for easily impelementing Ajaxed upload interfaces.
It comes with ready-to-use server-side code for PHP, ASP.NET & Coldfusion.

The script doesn't require any JS library to run & compatible with any of them (the example code uses jQuery).
As the upload function is fired with JavaScript, it is possible to use any object/image as the upload button which makes stying much easier.
AJAX Upload provides access to every level of the upload process (before, after, onComplete) for a better customization.
Requirements: PHP, ASP.NET or Coldfusion
Compatibility: All Major Browsers
Simply-Buttons v2 is a technique to create good-looking & cross-browser buttons that is inspired from:

The buttons are created with pure CSS and, optionally, improved with JavaScript (code is provided).
They fit to any text & come with 3 states: inactive, active and hover.
P.S. Their compatibility is tested on IE6 IE7 FF(PC/MAC) Safari SafariMobile Opera(PC/MAC).
Requirements: No Requirements
Compatibility: All Major Browsers
Chroma-Hash is a jQuery plugin that aims to offer a better password input experience.
The Problem:
A standard password field replaces the entered characters with "●" characters. The problem is "we never know if we made a typo or not until the form is submitted & a reply is received from the server".

The Solution:
Chroma-Hash, "converts the values entered" into a colored visualization.
A user filling the password field can easily recognize that if the colors are the usual equivalents of the password or not. And, anyone who sees the colors won't have any idea what the actual password is.
The script can also be used to visualize password confirmations (password & confirm password fields).
P.S. A detailed info on the method & security concerns can be found at the developer's related post.
Requirements: jQuery
Compatibility: All Major Browsers
Validatious is an unobtrusive & easy to use JavaScript form validation library that does not depend on any JS frameworks.
It has built-in validators like numeric, e-mail, URL, max/min char, etc. & custom ones can be created.

Using the library, it is possible to create chained validation rules like: validate( "email".is("required").andIsAn("email") );.
How and when Validatious does validation, how it displays errors & more can be controlled.
The library supports multilingual error messages with the help of a language file or overriding pre-built ones.
Requirements: No Requirements
Compatibility: All Major Browsers
GBCF-v3 is a free PHP form script that offers a nice level of accessibility & security.
The script has a valid semantic markup & does not use JavaScript. It is screen-reader optimized & keyboard friendly.

In means of security, the form asks a question to the user & expects the right answer to complete the submission. Also, an anti-flood control option can be activated to prevent multiple submissions from an IP & the number of blocked attempts can be seen.
The script is smart in many ways like "changing a form legend of a form also changes the e-mail sent" or no need of using the "back button" to fix the errors.
It is multilingual, has 20+ ready-to-use language files & can be customized easily via CSS.
Requirements: PHP
Compatibility: All Major Browsers
Tutorialzine is sharing a nice tutorial with source on creating a fancy Ajaxed contact form that is built with jQuery & PHP.
The form is unobtrusive & has a server-side validation which makes it degrade gracefully when the JavaScript is turned off.

It takes advantage of 2 jQuery plugins:
and a PHP class:
The contact form also has a basic captcha which works by asking the sum of 2 random numbers.
To check a demo of the form, click here.
Requirements: PHP
Compatibility: All Major Browsers
In some cases the standard HTML list box doesn’t offer a good usability like the need of scrolling or using both the keyboard & mouse.
MTMultiselect is a paginated & filterable multi-select widget built with MooTools.

The user can easily see the selected/non-selected items & can get all the functionality with only using the mouse.
The widget can be styled completely with CSS.
For a demo, click here.
Requirements: MooTools
Compatibility: All Major Browsers
jQuery UI Multiselect is a widget that converts html multiple select inputs into slicker interfaces.
It makes searching within the options possible which is very functional for large lists & selected items can be re-ordered by drag’n drops.

It can display the number of selected items & for an easier selection, there are select all/deselect all links provided.
The widget is unobtrusive & and be styled with ThemeRoller.
Requirements: jQuery 1.3+, jQuery UI 1.7+
Compatibility: All Major Browsers
VanadiumJS is an intuitive-yet-powerful jQuery plugin for easy client-side validation.
It supports Ajax & regular server-side response results. The rules to be applied can be defined in 2 ways:
- JSON structure
- inline markup

Some of the default rules include:
- presence
- a special format
- numbers (integer, float)
- length
- acceptance (checkboxes)
- & much more..
VanadiumJS offers various customization settings like, ability to validate-as-you-type or validation-on-submit, waiting x seconds before validating as-you-type, etc.
Requirements: jQuery
Compatibility: All Major Browsers
Elijah Miller is sharing a very nice script, inspired from the iPhone-style-checkboxes for jQuery by Thomas Reynolds, for creating iPhone-like toggle switches with Prototype.
It is a very flexible resource as:
- variable sizes of switches are created automatically
- has support for dragging
- sliding labels
- offers iPhone compatibility

How To Use It?
It converts the visual output of a checkbox & displays the standard checkbox when JS is disabled (unobtrusive).
To make it work, calling a simple function mentioning the ID of the checkbox & values is enough:
new iPhoneStyle('#variable_size_a_b', { checkedLabel: 'A', uncheckedLabel: 'B' });
That’s all.
Requirements: Prototype, Scriptacoluous
Compatibility: All Major Browsers