The Rails plugin directory now has an XML API. Based on inspiration from David's article, Discovering HTTP #1: The Accept header, all of the views now have a respond_to block that will return the HTML with layout to a browser or XML to a client specifying application/xml for the Accept header. Now we just need someone to write a plugin for Textmate to use the directory to find plugins. :)
For plugin authors, I've added a bit of RESTful goodness. If you PUT an XML blob (see the sample XML file) to http://agilewebdevelopment.com/plugins/new, you can script the publishing of your plugins. Since there's a fair number of people watching the plugin feed, this is an effective and pain-free way to get the word out about your new plugin.