I've just installed a new WP Plugin – WP Sales Graphics. It's rather neat.
The simplest way to explain what it does is to show you by example.
All the "boxes" below were created using the plugin.
Except for a few little quirks, it's extremely easy to use. I can re-use any of the boxes in any post by simply inserting a code, and I can update all instances instantly by editing the box via the plugin. Nice, eh?
Video Optin Box