ESO lacks a lot of the basic functionality of older MMOs. Fortunately, addons largely make up for it. By now the ones I use are generally stable and increasingly useful. I favor basic quality-of-life, information, and crafting addons, so you won't find PvP or combat stuff on this list.
I watch ESOUI for new addons and use Minion to keep them updated. It's stable, from a trusted source, and not riddled with trojans I swear.
Borrower and Lender: Shuts up bank NPCs and bards.
Wykkyd's Framework: If you get nothing else, get this. It includes a data bar, chat background and fade prevention, subtitles, auto-sheath, and macros.
Wykkyd's Quest Tracker: Replaces the single-quest tracker with an expandable/collapsible multi-quest tracker.
ChatMultiWindow: Allows multiple chat windows. Vital for RP and multiple guilds.
SpamFilter: Blocks spammers.
HarvestMap: Marks discovered gathering nodes (including chests!) on the map and compass. Allows you to filter by type.
LoreBooks: Marks lore books on your map.
SkyShards: Marks skyshards on the map.
TreasureMaps: Hate hunting treasure but love the goodies? Cheat!
Undiscovered: Shows points of interest, thus ruining the joy of exploration. I turn it on for zones where I'm missing one little thing.
ZrMM: A minimap. It ain't perfect, but it's all we got.
Advanced Filters: Adds sub-filters to inventory, bank, and gbank.
Crafting Material Level Display: Tells you what level range those runes are for.
Roomba: Guild bank stacker (guild banks no longer auto-stack because bots).
Show Motifs: Puts an icon next to equipment showing what racial style it is.
Wykkyd's Outfitter: Lets you save and load item/skill bar sets. These can be bound to macros if you have Framework.
AI Rearch Grid: Displays a table of known crafting traits and styles.
MultiCraft: Shows a slider to craft/deconstruct x items instead of clicking thirty times. Really speeds leveling.
Research Assistant: Put an icon next to weapons/armor showing whether or not you need its trait.
Softcapinfo: Displays the softcap for each stat, and how many points are lost to overcharge.
SpentSkillPoints: Displays how many skill points you've spent in each line.
RavenDT's Chat Logger: Right now it's just an alternative to /chatlog, but the author has promised that, "Next features will include the ability to choose which channels you wish you monitor (and which ones you don't)." Worth keeping an eye on.
Wykkyd's Mailbox: ESO doesn't allow you to mail your own characters. Wkkyd's Mailbox provides a work-around by automatically returning any message with the subject "bounce" or "return".
