Data broker plugins are addon threads for displays using LibDataBroker. A data broker display like Fubar, Titan Panel, or my personal favorite Chocolatebar is required to use data broker plugins.
Many plugins display additional information when you mouse over them and/or have drop-down menus allowing you to clean up your user interface yet still have quick and easy access to everything. By adding plugins you can set up a broker display mod to show virtually anything you want exactly where you want it.
Creates a bar at the top or bottom of your display where other addons called broker plugins can display things like your fps, latency, gold earned, and much, much more.
Ara Broker Money
Ara Broker Tradeskills
Another handy addon from Ara. This one shows you all your tradeskills on all characters. It shows cooldowns, including which ones are up and how long it will be until the others will be up again. You can also open and view the tradeskills for any character on the account.
If you're looking to find more broker plugins there's a nice big list of broker plugins over at WoW Ace complete with pictures for most of them. Mouse over the thumbnail pictures there to see larger pictures.
Addon Control Panel isn't a display broker or plugin but it comes in real handy for turning various mods on/off and reloading the UI without leaving the game... Like you'll be doing when trying out a bunch of new data broker plugins.