I think Deadron may have already requested this, but just in case he didn't, I will...

It'd be useful to be able to query an icon and get a list of all the icon states it offers. E.g.:

mob/proc/Die()
if("corpse" in icon_states(src.icon)) spawn Decompose()
else del src

Another example: I'd like to design different types of hair the user can pick (red straight short, long wavy black, etc.) and provide the user with a picklist of available "do's," without having to explicitly register each icon state by hardcoding it in the application.

Anyway, not a terribly high priority, but I think it could be quite useful!