A semi automatic .22 LR rifle. Seriously. No more AK's and Desert Eagles. Low kick, low noise, low shooting fatigue, lightweight, ammo all over the place.

As much as I love zombies (See: Zombie company http://www.facebook.com/UndeadSocial) they are becoming a trope of video games.

Do something different. For example, making find ammo realistic. Not like Left 4 Dead where you can find stacks of 7.62X39mm NATO laying around. Heavier ammo will produce heavier recoil, more noise, more flash, weigh more, and you will be able to carry less. Military ammo will be harder to find as people will likely scavenge downed military vehicles and patrol members, and the other stuff will most likely be guarded. This would make lightweight civilian effective. However, .45 caliber rounds, .308, etc. will do more physical damage (knocking back/toppling enemies) and will remain more accurate at long distances. Also, if you're going to give a gun like the P90 that uses a rare ammo (5.7X28mm) make that ammo actually hard to find.

A long stick with a spike on the end would be great if well implemented. If a zombie is toppled, on the other side of a fence, etc. you can just push the spike through its eye and kill it.

Make big weapons (sledgehammers and fire axes) do a lot of melee damage and knockback but hard to maneuver in close and very deadly to make a mistake. This would give hatchets, knives, and even frying pans their proper place.

It would be really great if you could have a system for melee damage with firearms based on the weight and composition of the weapon. A heavy weapon that slows you down could be a good bashing weapon, but a Barrett .50 cal would be too unwieldy to properly swing.

Also, a real condition for fatigue would be great. Your stamina can only regenerate to a certain point without resting or sleeping/stopping to eat.

Try giving weapons practical uses. For instance, an axe can knock down a door, a crowbar could break a window or pop open a car door, a machete can hack through thick forest... something to give realistic depth to the weapon. I might want a machete until I get into an urban area and find a crowbar is much more useful for popping doors for loot.

My post may seem not entirely on topic, but I've played a lot of zombie games and I see all the same weapons all the time. It's what they do with them that never changes. I used to play a Half Life 2 mod called Zombie Panic! Source. In it, you start with a melee weapon and a pistol with a full clip and 10 spare rounds. Every gun, weapon, or bit of ammo you grab slows you down. The guy with the magnum and 18 rounds can stay mobile and headshot zombies for instant kills, but can easily be overwhelmed. That's where a guy with an AK and 100 spare rounds comes in. It also helps convince players to share weapons so they're not dragging at a snail's pace and get picked off.

Your weapons don't have to be unique. I still see it as "swingy thing, shooty pistol, short range shooty thing, sniper shooty thing, stabby thing". Doll it up and make sure each thing is well thought out and given more depth than "what do you want to beat zombies to death with?"

Then focus more on the above than on what the specifics of the weapons are. It would be really great if the survivors had a "standard issue" weapon. Like a metal pipe with a big metal ball on the end and a retractable knife on bottom for finishing them off. Something unique and instantly recognizable. Or maybe different factions have their own weapons: One group uses machetes as standard issue, one uses night clubs and swarms the enemy, one group specializes in explosives, one group trains with knives. Each of these groups could manufacture their own weapons that would be unique.

Also, let me know if you need help with music and maybe sound. I'd like to talk with you if you think I could help.

Chemical stuff: acid smoke to burn their eyes, their skin, reduce their "life" by degeneration, insect swarms, sprinkles, barbed wire, stuff to make them attach each other (probably by smell as human blood or sweat), stuff to disguise as them (by smell and looks)...

Make any form of physical contact a necessary avoidance, that even a spit of blood can condemn you, no melee attacks anymore.

Build had to get to hideouts for the survivors. Like the top of a building with all entrances blocked and you have to cross from another building on a thin surface and holding a rope to equilibrate and not fall, as zombies would always fall. It's also a weapon to keep luring them to such death.

Traps would be cool. Bear traps to catch them and eventually remove their leg. Pit falls to collect them to dispose of them more easily. Moats, acid pools (stolen from above), explosions (black powder jars and the such). You could have ingredients found in a house to make explosive, incendiaries, and smoke grenades. For example, fireworks could be pretty awesome for a more lighthearted moment.

If you're going for a sim, please do stay away from Chainsaws as a primary melee weapon.

Also, Trench knives are pretty BA

Just go with the best weapon for fighting a zombie hord, the one everyone should choose: a katana.

Disclaimer: no seriously it does not fit your simulation requirement but i'd really enjoy fighting zombies with a authentic katana

For a minute I thought this was weapons used by the zombie hordes.