Displays a popup window (css layer) above the fold that shows new posts and comments since your last visit. Managed with cookies.
<h3>News</h3>
Fixed compatibility with wordpress 2.3, which also breaks compatibility with 
anything earlier. For that refer to <a href="http://svn.wp-plugins.org/new-posts-popup/tags/0.2/" rel="nofollow ugc">version 
0.2</a> of this plugin.

New posts popup

Displays a popup window (css layer) above the fold that shows new posts and comments since your last visit. Managed with cookies.

AbroadPal

Notification Widget offers you the ability to insert and fully customize an overlay widget for your website, blog, etc.
You can easily change all settings of the entire overlay in the Dashboard. 
There are the following settings for you to change:
Overlay Style: 
– colors of bar and content frame background 
– text of the content frame and bar
Overlay Layout: 
– distance of the close button to the borders 
– size of the close button 
– height of the bar 
– height and width of the content frame 
– widget position (X- and Y-axis)

Notification Widget

Notification Widget is a overlay allowing you to get a individual overlay for your website.

New posts popup vs Notification Widget