WP-FFPC
WP-FFPC is a full page cache plugin for WordPress, using APC or a memcached server for backend.
WP-SlidesJS
Adds a shortcut function to WordPress to create Slides JS slideshow from posts of a category.
Open graph headers
Open Graph Headers can extend any WordPress theme with open graph headers.
The plugins extends wp_head() and language_attributes() functions.
WP-Galleriffic
Yet anoter gallery plugin for WordPress. Supports WordPress attachments or Flickr sets as gallery, has it’s on cache and based on Galleriffic. My own portfolio (link above) is provided by this plugin as well.