For my premiere debút into the world of jQuery plugin development, I've written a little plugin called text separator. As I wrote on its jQuery project page, this plugin:
Lets you separate a text field into two parts, by dragging a slider to the spot at which you want to split the text. This plugin creates a horizontal slider above a text field. The handle on that slider is as long as its corresponding text field, and its handle 'snaps' to the delimiters in that text field (which are spaces, by default). With JS disabled, your markup should degrade gracefully to two separate text fields.
This was designed for allowing users to enter their 'full name' in one input box. The user enters their full name, and then simply drags the slider in order to mark the split betwen their first and last names. While typing, the slider automatically drags itself to the first delimiter in the input box.
Want to take it for a spin? Try a demo. You'll see something like this:
Text separator screenshot