Addons I use

Advanced Tradeskill Window --- If you tradeskill at all you need this
DotTimer --- Timing for dots and cooldowns with other misc events thrown in, a bit complicated for a simpler timer use ClassTimers
AutoProfitX --- Auto sell grey items to vendors has a customizable list if you want to autosell other items
AutoTurnin --- Pretty much does what it says
Bagnon_Forever --- Remembers what your other characters has in bank and inventory, works with Combuctor
Bagnon_Tooltips --- Lets you know who owns what works with Combuctor
Bang!_Anti_Spam --- Filters out gold selling spam and reports the offenders
BGDefender --- Small window with buttons letting you say in BG chat how many are inc and to what place "5 are inc to Blacksmith"
Cartographer --- Map addon with lots of modules, to many to list here
Combuctor --- Combines your inventory into one large search able window with tabs to sort gear by several methods
CooldownCount --- Puts a number time on button to countdown cooldowns
CraftLists2 --- Lets you sell your tradeskills easier and allows others to search your tradeskill recipe list
DeadlyBossMobs --- Warnings and alerts for top end instance Boss Mobs also a BG module
DoubleWide --- Turns your quest log into a two paned window for easier reading
eeShards --- Keeps track of soulshards can be set to delete shards above a certain amount
FishingBuddy --- Help keep track of what is fished where as well as simplifying using lures and casting
Gatherer --- Keeps track of resource nodes and displays them on world and mini map
InfiniBar-2.0 --- Lots and lots of extra bars you can configure anyway you want
LightHeaded --- Simple addon that displays quest information and comments from http://www.wowhead.com in game,
MobInfo2 --- Searchable database of mobs you run into with hp/mana, loot and other info, can be displayed in tooltip
MobMap --- Exactly what is sounds like, map of every mob anyone with this addon has ever run into
NotesUNeed --- Note program that can display info on tooltip with a searchable database
nQuestLog --- Very nice quest tracker in conjunction with MobInfo, MobMap, Lightheaded, and TomTom will make questing a breeze
Outfitter --- Change your outfits as you need with scripting that allows you to auto change as warranted, exp PvP set for BGs
PassLoot --- Will pass or roll need/greed on loot depending on rules you set up
RateingBuster --- A tool for item comparison shows if that loot are thinking of rolling on is better or worse than what you already have on
Routes --- It will allow you to draw lines (routes) along preselected gather-node configurations on a particular worldmap
SimpleAssist --- Pretty much what it says
TomTom --- GPS for WOW, pops a floating arrow on screen then leads you to your destination.
WarlockAlert --- Alerts you to Nightfall or Backlash procs