Assuming you have this on PC when it is released, the chances are that there will be mods made available for it.

As vanilla L4D is going to feature a limited selection of weapons (great idea, IMO), I ask what additional weaponry you'd like to see included.

From what I've seen so far there is:

Pump action Shotgun
Uzi

M16
Ruger Mini-14
M4 Super 90 shotgun


Pistol (can be dual wield)

Molotov
Pipebomb

What else would you like to see added, because someone will.