Version 5 of this well-regarded collection of Automator Actions supports both CS4 and CS5, and adds bug fixes, feature enhancements, and three exciting new actions for easing multi-picture layouts. Diptych and Triptych automate the process of creating two-up and three-up layouts, while Contact Sheet automatically generates contact sheets of thumbnails, with or without accompanying metadata.
To control Photoshop from Automator, you need to install Automator actions that allow Automator to take command of Photoshop, and this package is the largest collection of Photoshop actions available. The latest version offers 95 actions that give you access to just about every Photoshop command, as well as a few things that aren't available in Photoshop, such as the ability to copy IPTC metadata to Spotlight comments.
While Photoshop's Actions palette provides an incredible amount of automation power, its reach doesn't extend beyond Photoshop's features. With Automator, you can create automation workflows that span applications. So, you can define a workflow that automatically processes images, uploads the results to an FTP server, and then burns final images to a CD.
A sophisticated set of Filter actions let you sort your images based on orientation, IPTC keywords, EXIF metadata, color mode, and more. So, you can create workflows that process different images in different ways depending on their characteristics and metadata. This type of branching and comparing is not possible with Photoshop's built-in actions.
Finally, if you've already built a lot of Actions within Photoshop, you don't have to give those up, because you can trigger Photoshop Actions from within Automator.
And it's free! Mostly.
A basic set of 41 actions for CS4 and CS5 is available for free download (though donations are heartily encouraged). This set includes all of the everyday actions that most users will need. Users with more upscale needs can get the entire suite of 95 actions for $19.95. (Note that CS2 and CS3 packages are still available for free download.)