Dying Light -> State of Decay -> Dead Rising would be my 3 games probably. As crowded a genre as it can be, true gems are hard to find :/

the only zombie game i own and play is how to survive and unturned :P

nothing

My favorite Zombie game wasn't released on Steam. It was called Zombies Ate My Neighbors

One to give away? The Final Station (http://store.steampowered.com/app/435530)

Dead Island in Coop with a few friends and beers. Really good.

State of decay is my favorite. DLC is garbage, but the main game is a lots of fun.

Resident Evils and… well, that's about it. Still haven't found any other game involving zombies that looks even mildly interesting.

Dead Rising 2
Dead Island
Resident Evil 4 and 5
Nation Red
Zombie Driver
State of Decay
Dead Frontier
How to Survive (the tutorials were the best part)
Fort Zombie
Contagion
Zombie Panic Source
Zombie Master (never was able to play it but loved watching, the concept is incredible)
Counter Strike Nexon Zombies
Counter Strike 1.6. and Source with zombie modes (oh the memories)
The rest are flash games from Armorgames.com and\or elsewhere

Sonny and Sonny 2 (you play as a zombie but their nothing like Zombies but you do occasionally encounter actual Zombies that were not so fortunate as Sonny was)
The Last Stand 1, 2, Union City and Deadzone
Decision 1, 2 and 3
Rebuild 1 and 2
More Zombies
Road of the Dead 1 and 2
Lab of the Dead
Dead Frontier Outbreak series
Flaming Zombooka 1 and 2
Crush the Castle 2 Zombies mode
zOMGies 1 and 2
Necronator 2
Zombie Last Night 2
Zombotron 1 and 2 Time
Raze 1, 2 and 3 (aliens use Zombies against you)
Zombie Situation
Earn to Die 2012
DayTraders of the Dead
Toxie Radd
Zombo Buster
The Breach (just like Dead Space)
Headless Zombie
Infectonator Hot Chase
Zombinsanity
Earn to Die 2012 part 2
Infectonator Survivors (completed on steam, buy it to support devs if you like the incomplete version on armorgames)
Roadz
Zombie Riot
Tequila Zombies 1, 2 and 3
The Awakening
Don't Escape 2
Zombo Buster Rising
Dawn of the Celebs 1 and 2

Dead Trigger 1 and 2, Unkilled are awesome zombie mobile games, there's probably more good ones like the Walking Dead ones I've been meaning to play.

Might be more but I'm bad at remembering stuff.
Highly recommend all of these, flash games are games too.

i really like 7 days to die

Dead Island and State of decay.

N A T I O N R E D

Dead age

I played only a few zombie games to be honest
The Zombie Shooter games (started the first) are awesome arcade games. Lef 4 Dead 1/2 are great in it's genre - I think I would enjoy Dead Island and Dying Light, but I have problems running any of them - yay for computer. I like State of Decay's premise, but weirdly it worries me that if I read it well, eventually you'll die and lose, because that's how it ends. And for whatever reason, while it has a same promise, Project Zomboid looks awesome :) Maybe the less realistic presentation help to keep a distance from the game and not to get overly stressed

Left 4 Dead and Dying Light(if we count purely gameplay.. story was trash)

Dead Islands series, Killing Floor series, Left 4 Dead series, Dying Light and State of Decay

Stubbs The Zombie in Rebel Without a Pulse

Dying Light and Resident Evil 2:)

A favourite? Hm, I'm not sure if I have something like this. Well let me first check the zombie (or zombie-like) games I played on Steam:

• Left 4 Dead 1 & 2: They are good for some quick plays (about 1 hour). I enjoyed the first part more but different people have different preferences. For achievements I also played the competitive modes but I didn't like them (as in most games) for obvious reasons. Still have some achievements left T_T
• No More Room in Hell: Has this been mentioned already? It is a first person objective based zombie game (also free). First, on the bad side the animations, especially looking at other players, seem kinda strange sometimes. On the other hand it is probably one of those games where the feeling of getting overwhelmed by zombies is depicted pretty good. A bite does not necessarily kill you but can infect you (which leads to death later). It is also pretty hard due to limited ammunition so you have to fight with melee weapons most time. If you decide to try out pay attention to the server you are joining. Due to the average and really awfully low skill level of the general Steam user a lot of unlimited ammo servers have spawned which takes away half of the fun of the game.
• Resident Evil Revelations: That one was quite fun. You don't have to pay to much attention to ammunition, there are some weird monster types and the story is Resident Evil like kinda strange but the gameplay is nice.
• Resident Evil 4/5/6: Technically you don't fight zombies in them (beside a part of RE6) but they are still good games. Atmosphere wise RE4 probably is the best and Leon is just a smug bastard but I prefer RE5 more only because I played it in co-op mode which is a lot fun (although no horror anymore). Also think RE6 is a good game although a bit too much action for my taste. But I liked the intercrossing of the different stories. Bought recently RE0 & REmake so I will play them some other time. But I know RE1, 2 & Code Veronica X outside of Steam and I prefer the scarce ammo and fixed cameras gameplay over the third person action orientated gameplay starting with RE4.
• Dead Island & Riptide: Played them in co-op mode with my brother. And in this way they are really fun. Alone it is a more tedious experience. Also they are sometimes unnecessary long although if you just do the main quest they are rather short.
• Deadly Premonition (?): Does this belong here? There are long (far too long) passages where you have to fight some kind of undead demons/monsters. It is a strange genre mix of a game with an interesting to ridicolous storyline and an annoying ending (in my eyes). One of the more interesting games I played but beware the true horror of Deadly Premonition is to get it and keep it running.
• The Typing of the Dead: Yea, has also been mentioned before already. Also you are forbidden to say the z-word. The enemies are mutant. This is one hilarious game. A story which never tries to take it seriously. Obscure levels and settings and dialogues with an enourmos amount of cursing all leading to one stupid punch line in the ending.
• Teleglitch: Well zombies are the more harmless enemies of the game but it is still interesting if you can overcome the graphical limitations. Also one of the hardest game I played on Steam. I still didn't manage to beat it completely. And i really tried to.
• Dead Pixels: Just some mindless and fun 2d shooting fun with a lot of background references. Also has a co-op mode.
• Devil's Dare: Zombies and more. A 2d brawler game with different references. Co-op mode as well.
• Obscure: Most likely one of the best co-op experiences in a game I ever had. Nice setting and puzzles, have to pay attention to ressource management and one of the few co-op horror games with a kind of fixed cameras. There is a certain need to communicate with each other or it will end not so well. Technically no zombies, but plantlike monsters. Still really good.
• Deadlight: 2d platformer/puzzle game. One zombie game with the focus away from fighting. It is still interesting and something different.
• Clandestinity of Elsie: Just to mention it. It is a small and nice RPG maker game with focus on the obscure story and survival. Enemies are not that many but can kill you if don't pay attention.

Well, I do not talk about DreadOut since its concept is too far away from zombies (still great game). Hm, since choosing a favourite is difficult I try to at least answer the other question. Since I posess most zombie games that interest me I think I would like to see a giveaway for the lesser known games like: Obscure or Typing of the Dead: Overkill. Just check my wishlist. There is Guns, Gore & Cannoli which seems some like mindless zombie fun.

Zombie Vikings - It's like playing inside of a trippy cartoon...one of those hidden gems on Steam ツ

Resident Evil :)

Dark Souls. Yes.

Land of the Dead: Road to Fiddler's Green blown my mind when i was a kid
there is also dead island , state of decay , dying light , zombi ( zombiU)

ZOMBIE PANIC SOURCE
NO MORE ROOM IN HELL
CONTAGION
counter strike source zombie mod when you had to run from one end of the map to the other while other players got infected. not that stupid barricade crap
METAL ASSAULT?

one i would like to see in a giveaway... i dunno all the recent ones seem like shit to me. hurr durr multiplayer online apocalyptic world fight other players while zombies and starvation hurr durr Day Z etc

I'm interesting in Zombie Shooter, Zombie Shooter 2 etc. I have no idea where people keep posting those games as GA from here, not in any bundles\sales that i'm aware of