I had a real hassle of a coolant leak like this. Only applicable if your engine has a FWD water pump on it though. There's an o-ring sealing between the main body of the water pump, and the steel pipe that comes out the back of it and runs along the side of the block. That o-ring had got too old and hard on mine and no longer sealed.
If it's a RWD pump, I'm out of ideas.
Best bet is to pull stuff apart until you find it leaking. It is helpful to use one of those pumps to pressurise your radiator without having the car running. All workshops should have one.