If JavaScript is available the linked file gets shown in a new layer - if it is an image just as the image, if not inside an IFRAME. DOMinclude automatically positions the popup where the original link is and adds a text prefix to the original link telling the user how to hide the layer again.

A javascript class allows you to add window in a HTML page based on Prototype using innerHTML to load content.

AJX poop-up displays a message at the center of the screen and disables all other page controls until the message is closed.

An inline Pop-Up with Savvy.js and to spawn a pop-up and some JavaScript coding to input some data into it.

These popups use unobtrusive JavaScript and CSS to trigger the pop-up. They are searchable, accessible and only one pop-up stays open at a time.

These popups resize themselves to content of unknown size.

Non-standard alerts to notify the user of a problem with data they had entered. Uses a DIV overlay and javascript to parse through the information. Here's another implementation: Acejs.com - AceJS Alert.

Create an alert message in your post, with the class “alert”, for an indented background image positioned vertically half way down the alert paragraph.