An easy way to create your web site's favourites/shortcut/bookmark icon in Photoshop. FREE, $5 donation suggested if you love the plugin. (MacHouse has a video tutorial on making a favicon.)
(If you're looking for a plugin for OS X 'icns' icons, try Zonic IconLab.)
This plugin lets you grab image layers from any PSD/PSB file. It's faster than opening the whole PSD in Photoshop, if you just want a layer. Also, it lets you open PSD created by the newest versions of Photoshop, in older Photoshop versions that cannot read them directly. Most importantly, it can usually recover image layers from corrupted PSD files that Photoshop won't open (if Photoshop opens with damage, this plugin recovers a more intact image).
FREE - small donation suggested if it saves your day/sanity/job.
Improve throughput of your .img files for use in Electric Image Animation System in excess of 100X! If you work in EIAS Animator you cannot do without this one. A typical benchmark saving 57MB file:
FREE, $5 donation suggested.
File Format plugin that opens and saves 24-bit WebP images (Google's compression format for images on the web).