The following script is a single interface for pre-validating any HTML form. It lets you validate your form data the way you want, while handling the rudimentary tasks itself.

1) Change just one variable to make it work with $_GET or $_POST or $_REQUEST.

2) Name which elements are 'required' all at once in a hidden HTML text input.

3) Easily provide field descriptions in hidden HTML text inputs that you can use to print error statements.

4) Call a single function to print out error statements that you can easily style with CSS.

5) It automatically checks if fields marked 'required' have been filled out.

Most of the pre-validation code is from PHP 5: Unleashed by Sams Publishing. I found it extremely useful for a recent project. Sharing it here, I removed some unnecessary functions, and tried to simplify some points.

All the comments are my own; hopefully I provided more than enough explanation.

Prototype's Form.Methods library has a nice piece of code called 'serialize', which, if passed with the optional 'hash' parameter set to true, will convert an HTML form into a Javascript Object.

I was dismayed, however, to find that there was no way to reverse it; just as simply load a form using a Javascrip object.

So, here's one. enjoy.

libNog is a 9k library to provide somewhat easier browser-independence. It is not yet complete, and will be continuously revised. It grew from this snippet, and is still growing as I find things I use often.
Presently, libNog features:

A way to browser-independently get an XMLHttpRequest object.
A set of simple methods for GET, POST, HEAD, and to include other Scripts.
Simple methods for className control
A completely abstracted form of getElement*
Browser-independent methods for attaching and detaching event handlers
An event-normalization routine
A simple one-command 'Stop the Event' routine
And the big one: A simplified Class object by which classes can be built in JavaScript.

The above link will point you to the API documentation and history of libNog, as well as where to download the library.

ZeroField

AJAX: In situ edit
A simple edit in place using Prototype, based on the tutorial @ 24ways.org

This is a correct way to do login form auto-focus, checking to see if either username or password have focus already. This prevents someone from typing a username hitting TAB, then having JavaScript chime in, resetting focus to Username while user is typing in their password. In this case, the password is appended to the username which is in plaintext.

I use this in my AJAX as a quick way to get the Value of the selected item in a Select HTML object. If nothing is selected, it returns zero.
(May be basic to y'all, but maybe really usefull to someone else).

Simple chatting script to be placed on a corner of a website
Also a good example how to use ajax.

Set a word or phrase in an input field, clear it onfocus

This is a simple script to provide basic cross-platform XML request functionality in Javascript. It's meant to be the core component in any AJAX style framework. It is not an instantiable object, but instead is a namespaced microlibrary.

Calling is easy:
XMLRequest.GET(uri, query, callback, fallback)
uri: The location you're after
query: an associative array of form data to provide via the URL
callback: callback function of the form myCallbackFunction(objXMLHttpRequest), which is called upon successful (response = 200 OK) retrieval of the XML data
fallback: myFallbackFunction(objXMLHttpRequest), which is called upon failed (response != 200 OK) retrieval of the XML data.

XMLRequest.POST(uri, query, form, callback, fallback)
Similar, but does the query using the POST method. 'query' is the URL-appended data, still in associative array form, and 'form' is the same for the POST data.