Coolant Leak

Coolant is leaking somewhere around the rear of my engine near the transmission (or that is where I see it run out onto the ground anyway). The water pours out as fast as I can pour it into the reservoir. Does anybody have any ideas or suggestions of what might be the problem or where it could be coming from? Would it require taking off the intake manifold? Can it be easily to moderately repaired by DIY? I recently replaced the thermostat myself. Currently I have the front-end raised up on jack-stands. Any help will be greatly appreciated! Thanks.