Definitely check under the intake with a flashlight like Ldub says.

I had a mystery leak too. Nothing was ever on the ground... There are a couple of metal pipes (heater tubes) that are routed beneath the intake. One plugs into the back of the thermostat housing and the other one plugs into the back of the water manifold "log". They each have a small o-ring on them that dries out over time and starts to leak. The valley under the intake makes a great bucket to catch this leakage. Then when you drive away it sloshes out, but in my case - didn't leak a bit (on the ground) when I was parked.

Give it a look & good luck!