Lol you created the topic and didn't answer yourself? Ok, I'll start. This is based on what I've played the most in the past couple years.
1) Dwarf Fortress. Amazing depth and simulation detail.
2) Terraria. Fantastic art combined with smooth gameplay and tons of content.
3) FTL. Simple on the surface, but the deep micromanagement and ship configuration possibilities provide lots of tactical options with very different play-styles.
4) Minecraft (hasn't been indie in years, but it was!). Billions of dollars can't be wrong.
5) Spelunky. The way I nostalgically remember 2D platformer arcade games were when I was young, but they were never this fleshed out. Get the freeware version first before buying the updated version on Steam.
6) The Binding of Isaac. A loving homage to Legend of Zelda's dungeon levels, filled with secrets and an absurd number of items that stack together in interesting ways that change how you play.
7) Mount and Blade series. The quest system has always been extremely rudimentary, but by largely ignoring it, I have logged hundreds of hours conquering the world and enjoying extremely satisfying combat mechanics.
8) Rogue Legacy. Solid platforming, with lots of unlockable classes and progression, and bosses and secrets and replayability.
9) The Banner Saga. Amazing sound and art direction, combined with novel "caravan" mechanics, "choose your own adventure" style questing, turn-based combat, and tough consequences, make this game completely unique.
10) Desktop Dungeons. Get the freeware version. Very balanced, minimalist design with lots of unlockable classes and races. Casual, simple to learn, boardgame-like turn-based gameplay with some surprising tactics emerging gradually overtime.
11) Crypt of the Necrodancer. Adorable twist on beat games with classic topdown turnbased action. Still in early-access.
12) Papers, Please. Awkward, claustrophobic, and a lot like like real work, this is a game that pressures you to fail until you give up.. or learn to actually get very good at your job. Moral choices struggle brilliantly against the games' unfaltering drive to make you a cog in its detail-oriented fascist wheel.
13) Starbound. Terraria-clone that lacks the art direction of Terraria, but which is also branching out and trying to do its own thing. Still in early access.
14) The Depths of Tolagal. Another freeware topdown turn-based retro game I love.
Bonus list! Recent highly-rated indie games I'm just now getting into.