Home rules:

- We wanted close combat to be at least a semi-feasible option. Currently, going into combat with any more than 2 zombies was pretty much a death sentence, so we toned the basic zombie down a bit by:
*Getting rid of Zealot, and replacing it with Fearless
*Giving zombies 1 close combat weapon instead of 2

- Horde:
If two or more zombies (or zombie units) end their move within coherency, they 'merge', and become a single zombie unit.
(It becomes a little tiresome keeping track of individual zombie units - it's much easier, and more firepower efficient, to shoot at a large blob of zombies. This rule is especially useful in the higher sets, when there can be in excess of 50 zombies on the board at once!)

- Slow:
Zombies are slow. Any zombie unit without the Fleet special rule cannot run, and can only assault 6''.
(You covered this in the main rulebook, however I took it a little further and restricted the zombie assault distance to 6''. We found the survivors we overwhelmed a little too easily if the basic zombies had an assault range larger than that.)

- Brainless:
Zombies are brainless, and have trouble adapting. All zombie units cannot move, run or assault the turn they spawn. Zombies that attack a barricade cannot move or assault for the rest of the turn, however, if there are other zombies nearby (which have not attacked a barricade) they may move through the broken barricade and assault as normal.
(We found the survivors were overwhelmed a little too soon if we didn't restrict zombie movement like this. This way, the survivors have a chance to adapt to the increasing number of zombies.)

- Re-enforcements:
A single model can be purchased for 10x it's codex points cost, and comes armed with either a laspistol and ccw, or lasgun. If it is a single-wound model, it receives an additional wound. (e.g- Guardsman would come with 2 wounds instead of 1) The model must spawn at a weapons cabinet, mystery box, or shop point.
(Just for fun!)

- Wire transfer:
Survivors can share points freely. It does not cost AP or MP to give and/or receive points from another player.
(Encourages teamwork)

- Shop point:
Survivor's can use MP to buy listed weapons. It's somewhat like your weapons rack, only with a larger selection. We made a weapons list for a variety of Halo weapons - I could send you stats and prices if you like.

- Catch!
Survivors can 'throw' weapons to team-mates within 4'' for 1 MP. The thrower removes the weapon from his/her model (not literally - but I'm not stopping you!), and 'passes' it to a survivor within 4''. The recipient can either equip the new weapon immediately, or place it in his/her inventory for free - no cost to MP. If the survivor's inventory is full, he/she must choose to drop one of his/her weapons, or not catch the weapon thrown to them. This can be done immediately after a survivor is downed (it is assumed they quickly throw their weapons to a team-mate before going down and drawing their pistol).
(This just seemed logical to us - and came about when I found myself with a gun I didn't need, and my brother did.)

- Automation:
When there is no zombie player:
*All fleet zombies must run, and must re-roll their run if the result is a 3 or less. Fleet zombies do not run if they are within 9'' of a survivor, instead they must try and assault the survivor. Fleet zombies must re-roll any charge roll of a 3 or less.
*All zombies move towards the nearest survivor.

- Tough Zombies:
When rolling for zombie spawning, for each roll of a 1, roll on the zombie table instead of placing a standard zombie. (See the word document attached)
(We've play-tested this table a bit, and I'm satisfied with it at the moment. Having tough zombies spawn on the roll of a 1 means that the survivor's aren't completely overwhelmed by large numbers and tough zombies, it also adds a bit of a challenge and some variety to the horde. Again, we haven't played COD zombies, so the zombies in the table may not quite be what you're looking for.