Sensor Question

Hello.

I was wondering if anyone had any insight on what sensor would work best for this application. I have a piece of plexiglass as a table top. On the underside of the plexi I wish to mount a sensor to detect if an object is on the table top. The object would be directly above the sensor. It does have to best frosted plexi but that is preferred. I have tried the Optical Detector / Phototransistor - QRD1114 from Sparkfun and it worked well until the table was in bright light/sunlight. So then I had some photocells sitting around and tried to use the two sensors together to detect a single object. It worked better. But I would rather not use two sensors for every single object detector I make. I have to rig up quite a few of these sensors. Something simpler is preferred. I have looked into modulated IR but I couldn't find a way to simply modulate the IR. I had a 555 timer laying around and make it work but then again I was looking for something simple. Any help is appreciated.

what about capacitive sensing?
i was able to detect glas through a thin rubber layer...

here we have some more details in the playground:
http://www.arduino.cc/playground/Main/CapSense

Are you talking about heavy or light objects? If the objects are heavy enough, you could use a strain gauge.

any object?
could magnets help?