Here is the full list of all 43 Over 9000 Zombies! achievements.
Kill 900,000+ Zombies!
Construct 1000 Turrets from random scraps of metal!
Derail the Waltz of the Undead!
Construct 100 automated turrets.
Vote for Zombie Thomas Jefferson, or don't.
Kill 90,000+ Zombies!
Collect 100 Power Ups!
Kill over 1000 zombie eyes!
The zombie world is independent of our will.
Abused patience turns to fury!
Health is the greatest gift, a close second is BRAINS!
Terror possessed me then!
If only he had the body of a horse...
A jail is an isolated system.
Zombie Napoleon meets his zombie Waterloo!
Kill over 1000 crabs!
Blood and Flesh can be trusted.
Get 15,000 damage per second!
Decreased Zombotropy.
Voted the greatest zombie of all time!
Quoth the Raven "Nevermore."
Get 30 kills per second!
Kill over 1000 zombie crows!
Don't call me slow!
Kill 9,000+ Zombies!
Your world didn't end!
No 8th symphony for zombie Sibelius!
You didn't donate your organs...
Kill over 1000 zombie dogs!
It didn't taste like chocolate ice cream either...
Not a wimp.
Lots of progress!
Participate in a multiplayer game.
You watched the world burn, and survived. It was kind of cool.
The army of the undead will march at daybreak!
Get 5,000 damage per second!
Kill 1000+ Zombies!
Green IS good.
Construct a turret from scrap metal!
You won that race.
Making some progress...
Get 10 kills per second!
The first day is always the hardest, except in this case, it's the easiest.