This shell script for Automator will automatically download any and all .zip files you supply, extract them, then remove the original .zip files. Feel free to replace .zip with any other specific file type.
Create a new service in Automator, set Service Receives Selected to "files or folders" in "Finder", then add a "Run Shell Script" to the workflow. Set Shell to "/bin/bash", and Pass Input to "as arguments", then paste the following in the script editor. Save the Service with a suitable name (Ie. Download WP Plugins).