You can already do what I'm asking for through the CVARS, but you need SV_Cheats set to 1. The problem with that is that anybody who knows how to use the console can do whatever they want when that's on. This plugin would allow admins to give things like health kits and weapons along with being able to spawn zombies on command, perhaps by toggling SV_Cheats from 0 to 1 and back very quickly.
The CVARS can all be found here, they're mostly pretty simple:
http://left4dead411.com/l4d_cvar_list.pdf
z_spawn tank/boomer/hunter/witch/smoker/mob controls zombie spawns
give rifle/hunting_rifle/pills and so on gives items