Text expander plugin. Just like popcorn. Click and pop.
Abbie Expander is a super simple implementation of Bourbon Refill's Expander in the form of a WordPress shortcode. Create expanders lickity split
Expandoo expands images when they are clicked, much like a lightbox, but without opening anything new.
Scans posts for Youtube URLs and expands them to show a playable video at the end of the post.
Scans posts for picplz links and expands them to show the image.
Twitpic Expander scans posts for twitpic URL's and automatically expands them and shows an image.