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