Depends what you want'm for. I'm currently using:

PvE/Trade:
- Master Merchant(MM)
- Quest Map
- Lorebooks
- Skyshards
- Awesome Guild Store
- Wykkyd's outfitter
- Destinations
- RaidNotifier


UI/PvP
- Foundry Tactical Combat(FTC)
- Exterminatus Gorup Leader
- PapaCrown
- KillCounter
- CyrHUD

Crafting/Others
- AI Research Grid
- FCO ITemsaver
- Harvest Map
- Potion Maker
- Shissu's LUA Memory.

My personal choices (I have a few more but these are what I consider essential):

- Combat Metrics:VERY detailed breakdown of each fight, including buff uptimes, incoming and outgoing damage and healing, and much more. Allows you to save statistics after a fight to review at a later time or compare with another attempt to check what's increasing or decreasing your performance.
- FTC (Foundry Tactical Combat): I use it only for the scrolling combat text and combat frames, as my DPS analysis is done through CM).
- S'rendarr: tracks your buffs/debuffs/DoTs in real time. Invaluable when you need to reapply them regularly and don't want to do it too soon - waste of resources - or too late - lower DPS.
- Alpha Gear: allows you to save gear/skill presets for different situations, e.g. one-button gear and skill swap between a trash fight and a boss fight.
- Autoinvite: allows you to "grab" people from guild or zone chat by setting up a keyword; it also makes it easier to disband and reinvite all group members, e.g. to reset and restart a trial.

- Master Merchant: collects statistics from your guild stores to give you an approximation of the real value of stuff. Be advised that it's heavily dependent on a good sample, so if you're in guilds with low sales you'll probably get garbage numbers.
- Advanced Guild Store: what guild stores should have been. Lots of filters and the ability to do text searches (though limited to the current results page due to ESO's API limitations).

- Destinations: lots of PoI on your map, including many that are achievement-related (random encounters, fishing spots, monster trophy farming spots, etc).
- HarvestMap: adds map pins for every node you ever harvest, so that if you're looking for a certain crafting material you can know the best spots.
- Skyshards and Lorebooks: because after making 8 characters I already know most of the skyshards by heart, and lorebooks are relatively easy to find, so just having the locations on the map to make sure I don't forget any won't hurt much; I wouldn't recommend it for your first playthrough.
- Lost treasure: adds map pins for treasure maps and surveys.

Cryptical wrote: »

On console, you have the flood of numbers that disappear in 0.25 seconds, and the power of your brain to track their relative size and color and location. It's not uncommon for a console Templar player to eyeball over two dozen numbers per second when jabs/sweeping multiple mobs.

Console players uber alles.

You should see the FTC text for a DK that has a full DOT stack ticking and try and decipher that lol