Dark but it doesn't release until the end of the month.
Check out http://www.desura.com/games/project-zomboid and http://www.desura.com/games/underrail
You're fired. Please gather your belongings. Security will be here to escort you out of the building momentarily.
I just don't get the appeal. I thought the narrator was interesting, the setting was cool, and the music awesome. But the action just didn't hold me and that game was ninety-five percent action.
The binding of Isaac
Don't Starve
Legend of Grimrock
Dungeons of Dredmor
Skyward Collapse
Evoland
Monster Loves you
Super Puzzle Platformer Deluxe
I thought Legend of Grimrock looked interesting, but I'm not sure how well my computer can handle it.
I really wanted to play Evoland for a bit, but I haven't read one positive thing about it since it's release.
I hear The Binding of Isaac and Don't Starve are awesome, but I can't find anyone to tell me why. The gameplay doesn't look like anything special from the tiny bit I've seen of it.
http://store.steampowered.com/app/200900/ and http://store.steampowered.com/app/70300/ are two good ones that haven't been mentioned.
World of Goo
It really amazed me how great that game was with the quality, puzzles, and such. Another game that's coming down the pipe is War for the Overworld which is a spiritual successor of sorts to the Dungeon Keeper series, that has been abandoned by EA since they took control over the studio that made DK. It might be best to wait for WFTO because it's still in alpha stages at the moment.
I can recommend these myself.
Binding of Isaac is a rogue-like mixed with elements from say, the original Legend of Zelda. IT's fun, challenging, and rewarding. With a REALLY creepy but awesome theme.
Don't starve is a survival game. You eat, fight the elements, build fires and shelters, kill monsters, make inventions, etc.
Legend of Grimrock is nothing short of [censored] awesome. It's an action RPG with 3D grid based movement. It's a throwback to games like Eye of the Beholder and Ultima Underworld.
Dungeons of Dredmor is a really cool rogue-like RPG. Randomly generated levels as you keep going down and the difficulty increases.
If you don't like minecraft or terraria, you are a lost cause.
http://www.gamesas.com/topic/1453273-the-unofficial-indie-thread/
Ignore him, he apparently doesn't understand opinions.
I haven't played it yet, but what I've seen of gunpoint it looks really fun. I'd check it out.
I enjoyed Atom Zombie Smasher. Unique premise and fun gameplay.
AI War: Fleet Command is a great game if you are looking for against AI RTS
Harvest: Massive Encounter is lots of fun
Capsized is very good albeit pretty short (about 4 hours)
World of Goo is great, I didn't see it mentioned.
EDIT: Apparently it was mentioned. Count me as seconding that opinion.
Legend of Grimrock is pretty good. The puzzles are pretty lame, though.
You should also check out Geneforge, it's a solid RPG series (there's 5) with fairly interesting lore and gray morality. The sound effects, graphics and interface are pretty darn ugly but I'm willing to look past that, but for an indie game that's over a decade old, it's holds up fairly well.