Your descriptions are fantastic, but you need to link to sources for each mod you discuss.
I took screenshots of the addons that I use most often and heavily rely on. I have edited each screenshot to indicate which addons are which so click on them to view highlights of each! Read below for a full list of my addons (: Well, not full because in the middle of listing everything, I've decided to take out the obvious addons such as QuestHelper. A few that may seem obvious such as Auctioneer or Atlas Loot, I would like to point out neat features that I really like ;D
AckisRecipeList: Scans any of your professions for missing recipes and the location of the recipe. ACP: Adds an "Addon" button to your main menu for easy access in order to enable or disable addons with a click of the "Reload UI" button. Aloft: Changes the size, colours, visibility/transparency, and information on nameplates. AtlasLoot: Lists the loot dropped from bosses or acquired from events. One thing I really like is that I can make a wishlist of items that I would like to roll for. Auctioneer Advanced: Scans the Auction House and stores its data viewable on item tooltips. I mainly use this add on to sort auction listings by PCT. BetterInbox: Opens all mail attachments. Butsu: Replaces and repositions the loot frame with a sleeker and smaller frame. Chatter: Highlights names by class colours, time stamps messages, indicate character levels, etc. etc. Similar to Prat, but smaller in size. DrainSoulTimer: Plays a sound and warns you either in chat, SCT, raid warning, to start drain soul. Plays a short "tic" sound whenever drain soul deals damage. Enchantrix: Numerous enchanting options. I mainly use it to check out how much mats are worth for an enchant and how much I should charge for an enchant in my profession window. Enen: Bypasses the 60 second limit on the chat flashing tabs whenever you receive a whisper. EngBags: Wonderful bag mod that combines your bags into one, auto sorts your items, has a search function, and allows you to view your bank from anywhere. I have tried every single appealing bag mod out there and this one is definitely the best. I have no idea why not many people use it ): EnhancedFlightMap: Shows all the flight paths and connections on your map. Displays a flight time in the tooltip and a timer during flight. EPGP: A DKP system my guild uses. I believe it's the fairest system out there, definitely deserves to be checked out. Examiner: An inspection mod that shows you the details of a character's gear, stats, talents, and arena teams. The best out there. FailBot: Really cute mod that announces in a chosen channel every failure occurred in the raid. Examples: Getting hit by Sartharion's Lava Waves, Kel'Thuzad's Shadow Fissures, Deconstructor's Gravity Bombs, General Vezax's Shadow Crashes. Fane: Really pretty and minimalist chat tabs. ForteXorcist: A package of addons very useful to warlocks. I also believe they have addons for other classes as well but I have not tried them out. Anyways, includes a spell timer, cooldown timer, soul shard count, soulstone tracker, summoning assistant, healthstone tracker, and CC announcements. InlineAura: Displays a glowing border around spells on the action bar that are already casted on either the player or on the target. Example: Haunt will have a glowing red border if Haunt is already casted on the target or Fel Armor will have a glowing green border if Fel Armor is already casted on the player. Very useful for a quick check if your Life Tap glyph buff is up. LoggerHead: Automatically /combatlog when you enter a chosen instance to log the combat. Lootster: Very helpful master looting addon that allows you to quickly announce rolls, view rolls, view winners, and announce winners. OmniCC: Displays a countdown on a spell on the action bar indicating its cooldown. Outfitter: By far the best gear organizer. You can save sets of gear you can quickly switch in and out of. My sets are: Spell Hit 10%, Spell Hit 13%, Durability (it takes off all my gear), Noblegarden (bunny ears and such!), Winter Veil (santa hat and boots!), Resilience (PvP gear!), Tank (Sartharion and 3 drakes). It will also automatically switch your gear when you switch between your duel specs. Overachiever: Addition features to to achievements that allows you to easily keep track of achievements in your zone, achievements requirements in tooltips of items you have to consume or use etc. RecipeRadar: Displays markers on a map of a chosen zone to show where a recipe can be bought. SCT: The best combat text mod I have used. Very useful for warlocks who are struggling to keep up the Life Tap glyph buff. It will show "[Life Tap]" whenever you life tap and "-[Life Tap]" whenever the buff fades. Tactics: Prints boss descriptions in a chosen chat channel. I do not believe it is updated for Ulduar but you can easily add more bosses to the file yourself. I personally edited every boss according to our guild's executions. Very useful when you have a new recruit raiding with you the first time. tekJunkSeller: Automatically sells grey items in your bags when you visit a vendor. teksLoot: Replaces the need/greed rolling frames with a more minimalist and prettier frames. Tenmetsu: Makes chat tabs flash whenever a message is sent, not only whispers. TradeTabs: When you open a profession window, it also displays tabs for your other profession on the side so you can easily flip between recipe books. Xperl: Definitely the best unit frames out there. I have tried all the popular ones but they were never satisfying. Although it may seem very ugly when you first use it, you can definitely take a few minutes to customize it to have the similar and popular look as Pitbull and others. Check out my screenshots to see (: One thing I love about this addon is that it includes a cast bar with latency indicator and also the useful distance indicator that fades someone's frame if they are far away (take advantage of it to quickly send out summons! or if you know you are suppose to be running away from someone with a harmful debuff, you can check if you are far enough from them in the first place so you do not have to spend the looking for the person and running the opposite direction!).