Everything said here and more so.
My thoughts:
Old glory civilians + westwind secrets of the third reich zombie heads = instant zeds.
(Actually Pappa midnight did this with just some limb repositions and a dead skin pallet so no need for the heads, though they do work well).
Any civilian can be positioned up as a nice zed, limb losses are always good, also good for changing zeds about too, (I have two of these so one lost an arm):
Figure list: from the top of my head:
Tengu miniatures: new little company, great zombies.
Hasslefree: Matt Lord's zombie minis and the character zeds as already mentioned.
Studio miniatures: obviously
.
Muskateer: three very nice modern zeds including Gene Kelly!
Heresy: fantasy, but with a little cut and shut will work fine.
Cold war: The dead walk range, great characterful minis large range.
Crocodile game: modern zombies.
Griffon: Not sure if they're still available and too much 'history' for some people.
Griffon and cold war zeds:
Griffon, cold war, Studio, crocodile and gw conversions:
Montage!!!
More on my zed thread, give me a shout if I can be of any help with this.
The Commander