Same deal here as in the other threads I created, except this time about indie games.
Incase you don't know what indie means, its short for indepent and it means that developer aren't signed up with any major game publisher like EA Games, THQ or Activision and instead publishes it themselves via Steam, Desura or any other service that support indie games.
And so, here are the ones I've played and enjoyed a lot.

1: Zombie Driver HD
This game puts you in the role of a survivor who must drive various vehicles through a city that's just been the site of some sort of explosion at a local chemical plant that's now spreading a virus that's turning people into zombies, you end up being contacted by the military who wants you to help them with various tasks, including finding other survivors and killing huge mutated zombies.
You can upgrade your weapons and cars in the game and they certainly will help a lot as the zombies will get tougher and tougher.

2: E.Y.E. Divine Cybermancy
A cyberpunk FPS with RPG elements set in the distant future where mankind has developed the technology to go to other planets and colonize them.
You play as a member of a group called the Secreta Secretorum that are waging a war against an oppressive federation who rule many worlds with an iron fist, but the federation isn't your only enemy.
Within the Secreta, there are internal struggles and it threatens to tear the group apart and you will soon be forced to take a stand.
Since it is cyberpunk, you can be certain of that there are augmentations to be had, most notably advanced hardware that allows you to more easily hack enemies and turrets and make them your allies.
Another thing is that the game was made using the Source Engine, Half-Life 2's graphical engine, and also focus a lot on co-op.

3: The Binding of Isaac
I'm certain of that almost everyone online know of this odd little indie game.
Really strange enemies, disturbing enviroments and more await poor little Isaac in the cellar and beyond as he seeks to escape from his religious fanatic mother who intends to sacrifice him on behalf of god.

4: Terraria
This game has been called by many as Minecraft in a 2D setting and it is actually rather fun to play.
Not to mention, you will face some rather disturbing enemies here and there, including The Eye of Cthulhu.
And of course, you can make your own little houses for both you and the NPCs that wander the area and also equipment for yourself to use.

5: Uplink
Remember the developer Introvision?
Well they made after the smash hit that was Darwinia, they made a new game that puts you, the player, in the role of a hacker for hire.
You will be undertaking jobs that may involve you hacking into a company's database and steal a file or even destroy one or erase someone's identity from the national database.
The game really pulls you in and makes you imagine that you're really a hacker who is doing all these jobs and getting payed for it.