This article is still a work in progress.
I am looking for a joomla extension that will pop-up a window the first time a visits a site each day. It needs to be fully customizable in appearance. I used to use Moo Pop Up but it doesn't appear to be available for Joomla 2.5.
NoNumber Modals
Selected Solution
http://www.nonumber.nl/extensions/modals
Free and 30 Euro versions
NoNumber makes a number of extensions that I use all the time such as ArticlesAnywhere and Sourcerer so I was encouraged to discover Modals.
Simple Popup
Free
Looked promising but it conflicted with the background image viewer on the site. Changing the Advanced setting: Load jQuery through Joomla to "Include" resolved the conflict.
This was the second-best solution. It's free and very basic. It's a plug-in and not ideal because it therefore requires adding some text into the article that you want the popup to appear on rather than having it dictated by a "show on all pages" type of approach. But it works fine and meets the purpose. However, I wasn't able to get the full customization of the look that I wanted without having to edit a javascript file to remove a border from the pop-up.
Multipurpose Popup
$10
http://extensions.joomla.org/extensions/style-a-design/popups-a-iframes/21764
Jdialog
is designed with accept / deny buttons to restrict access to a Web site but might be suitable if it can be customized enough.
http://extensions.joomla.org/extensions/style-a-design/popups-a-iframes/5129
Website Disclaimer Popup
$35
Similar in intent to Jdialog
http://extensions.joomla.org/extensions/style-a-design/popups-a-iframes/22316
System Popanywhere
http://j25.codextension.com/system-popup-anywhere-plugin.html
Mega Popup
http://extensions.joomla.org/extensions/style-a-design/popups-a-iframes/26196