There is currently a good bit of debate surrounding the effects of low levels of exposure to electromagnetic fields. Static Electric and Magnetic Fields and Human Health and Possible Health Effects of Exposure to Residential Electric and Magnetic Fields offer a lot of information on the subject. To answer your specific question about cellular radio towers, here are a couple of things to keep in mind:
- Cellular towers are transmitting at low power in order to limit their range (see How Cell Phones Work to understand why low power makes the cellular concept work). The power level from the tower is not much different from that of a CB radio.
- If you're worried about cellular radio waves, any potential danger would be much more worrisome for the users of the phones, where the transmitter is only inches from the head rather than hundreds of feet away.
To learn more, see How Cell-Phone Radiation Works.
Here are some interesting links: