A few user-contributed plugins, in random order:
GTasky - plugin for managing Google Tasks in Launchy. See also this blog post.
Launchy EC2 - a Launchy plugin to connect to EC2 machines quickly by autocompleting on the tags of the hosts.
LaunchyTomboyPlugin - A plugin for Launchy to put Tomboy note titles in the catalog. See also the announcement.
pylaunchygoogletranslate - provides quick access to the Google Translate API.
Some plugins that were posted to the project forum: