For me, I would like to have these
DrDamage (so it shows the spell damage )
http://www.wowinterface.com/download...-DrDamage.html
Omen Threat Meter (gotta have this if you group or raid )
http://www.wowinterface.com/download...reatMeter.html
Chinchilla ( it makes you map draggable and resizeable)
http://www.wowinterface.com/download...hinchilla.html
TipTac (make your Tip customizable)
http://www.wowinterface.com/download...93-TipTac.html
Mendeleev ( show additional info of an item )
http://www.wowinterface.com/download...Mendeleev.html
MiniMapButtonFrame ( collect your minimap buttons , so it won't be too mess
http://www.wowinterface.com/download...ttonFrame.html
Rating Buster ( to compare equipment)
http://www.wowinterface.com/download...ingBuster.html
PerfectRaid ( for raiding time)
http://www.wowinterface.com/download...rfectRaid.html
AlphaMap ( for map)
http://www.wowinterface.com/download...date.html#info
Lightheaded ( it is a must have, get wowHead.com info in game )
http://www.wowinterface.com/download...ghtHeaded.html
TomTom
http://www.wowinterface.com/download...32-TomTom.html
TourGuide ( for progress suggestion)
http://www.wowinterface.com/download...TourGuide.html
CarboniteQuest ( alternative quest helper )
http://www.wowinterface.com/download...niteQuest.html
Atlas ( for the instance map)
http://www.wowinterface.com/download...896-Atlas.html
Atlasloot ( for the possible instance loot)
http://www.wowinterface.com/download...tEnhanced.html
AtlasQuest ( for the instance quests )
http://www.wowinterface.com/download...FanUpdate.html
OmniCC (show count down of spell in the button )
http://www.wowinterface.com/download...36-OmniCC.html
DotTimer ( for DoT and cooldown)
http://www.wowinterface.com/download...2-DoTimer.html
Decursive
http://www.wowinterface.com/download...e2.1-Ace2.html
EaveDrop (combat log is collected into a small windows summarized)
http://www.wowinterface.com/download...EavesDrop.html
RangeDisplay ( it shows the distance between you and your target)
http://www.wowinterface.com/download...geDisplay.html
FizzwidgetAdspace ( it shows if the receipe on AH could be buy off vendor)
http://www.wowinterface.com/download...etAdSpace.html
Fizzwidget DisenchantPredictor ( if you DE a lot )
http://www.wowinterface.com/download...Predictor.html
Clique ( if you want to click and cast )
http://www.wowinterface.com/download...08-Clique.html
MikScrollingBattleText
http://www.wowinterface.com/download...attleText.html
FishermansFriend (for fishing)
http://www.wowinterface.com/download...ansFriend.html
Autobar (so you dont waste space for food, potion, water)
http://www.wowinterface.com/download...2-AutoBar.html
QBar ( Quest item bar only )
http://www.wowinterface.com/download...8645-QBar.html
MozzFullWorldMap ( for the unexplore map)
http://www.wowinterface.com/download...ansUpdate.html
Altoholic ( if you have more than one alt)
http://www.wowinterface.com/download...Altoholic.html
Trinket Menu
http://www.wowinterface.com/download...inketMenu.html
Outfitter ( for changing sets of clothes )
http://www.wowinterface.com/download...Outfitter.html
Gatherer ( if you are a herber or miner )
http://www.wowinterface.com/download...-Gatherer.html
Satrina Buff Frame 2 ( for the buff or debuff, save space)
http://www.wowinterface.com/download...ffFrames2.html
===
Trinity2 bar (my favorite actionbar replacement, but you might want to try bartender3 or bongo2)
http://www.wowinterface.com/download...tyBars2.0.html
X-PerUnitFrame
http://www.wowinterface.com/download...nitFrames.html
PitBull Unitframe
http://files.wowace.com/sw-p.html
FuBar2 and all of its little helpers (prob just some you would need
)
http://files.wowace.com/sw-f.html
there are more and more that I am sure others would suggest.
this is what I could think of so far
Don't try to install all at once, some might be in conflict of others
or it could make the whole screen messy since there are so many
Just choose one and see if you like it , and if you like it, then keep it.
Also, you should also check the Pick of the Week column ( Seerah does a great job of recommending
)
http://wowinterface.com/pickofweek.php