Look at your overflow tank, see if it's getting dirty or oily. That could indicate a serious problem. Also, change your oil and see if there is antifreeze in the oil. Another bad indication.
It may just be a tiny crack in a hose that starts spraying after the engine gets hot. If it sprays on the engine, it would evaporate instead of pooling.
Run the car and put the heater on and see if you smell something sweet.
you can go to the chain auto parts stores and rent a pressure tester. basically, you remove the radiator cap and attach this pump (cold engine not running). Then pump it up and you should be able to track down a leak in a hose, radiator, reservoir, seal, etc...