Addons I use are:
-X-Perl Unit frames
-Bartender 3 and auto-brindings(customisable action bars)
-Cycirlced (to skin and colour the default squareness of the action bars into something more interesting)
-Recount (damage/healing/etc meters)
-Omen (threat meter)
-Bagnon (collects all your inventory into a single space, far more useful than the default system).
-Fubar, w/ moneyFu, durabilityFu, Poisontimers, performanceFu...
-Rogue Class Timers (durations of SnD, Rupture, Saps, etc).
-Cowtip (for cutomising tooltips, moving them about and getting lots of rather handy info on mouse-over).
-ScrollingCombatText and SCTD (a more detailed, customisable and fun version of the default combat text).
-CritLine (records maximum hits and heals with your various abilities).
-Atlas and Atlas loot enchanced.
Not all viewable in that screenshot, but they are there. All should be obtainable from either Curse or Wowace.