Thanks everyone for your ideas. This forum is a great source of info!
I've tried all of the ideas, but everything looks ok. :(
The evap hose is not plugged (I blew air into the hose from under the car (with my mouth), and it was not plugged (air flowed very freely)).
The drain under the wipers was not plugged (I poured some water into this area, and the water quickly flowed out onto the ground thru the drain hole).
Sunroof drains also were not plugged.
All grommets look fine (I put the car on ramps and checked them all).
I then washed the car, spraying everywhere (under the car, in the wheelwells, at all sides of the windshield, at the door seams, etc), and nothing...
So now I'm really baffeled. The only far fetched idea is this: 1 week ago my wife had the car in a local shop for a smog check. Am I out of my mind, but is it possible that they poured water in the footwell to inspire new business? I'm not usually such a pessimist, but I'm running out of ideas. Ever heard of such a thing? :o
Thanks again everyone. I put it all back together, and I'll check it from time to time to see if it happens again.