I'm talking about stuff like gives you more icons on your screen like on this screenshot, http://thottbot.com/ss44826.

The screenshot you have linked, looks like  Titan Panel, and some options from the game interface menu.  Titan panel is the small bar at the top and bottom of the screen, you can set it to show things like amont of gold you have, number of free bag slots, ammo, xp needed to level etc..  The extra action bars on the side and the extra bar on bottom can be set by going to the game menu, choose "interface" then go to the "advanced" tab.  On the top of the screen you can choose "show action bar 2" "show right action bar" and "show right action bar 2".  So if all you want are the extra action bars, you dont need any add ons at all.  Hope this helps :)

not sure i this is the kind of add0n that you mean, but i use the Ganklist. propably the best add0n(especially in pvp realms)

when you're killed outside of the arena/BG's, you get the option to add them to your 'ganklist', then whenever you highlight that player you will know if they have ganked you before. it's allowed me to get revenge on alot of players that killed me when they were higher lvl than me :)