Matt, there is no command to show a list of 'plugins' for ULX.
You can type "ulx help" in console to see what commands you have access to, many of those coming from different files within the ulx addons folder.
From server console, "ulx debuginfo" will write a file to the server data directory of various information including the /addons from your server, including ULX.
What specifically are you looking for?