Cell phones and cancer?
I think this cartoon from Calamities of Nature covers the main danger of cell phones, but basically radiation (cell phones, microwaves, etc.) below the visible range of the electromagnetic spectrum, won't cause DNA to mutate. As long as your blood is flowing, it won't even cook your brain.
The article "Cellular Telephones and Cancer: How Should Science Respond?" in the Journal of the National Cancer Institute.
points out that "all known cancer-inducing agents—including radiation, certain chemicals, and a few viruses—act by breaking chemical bonds, producing mutant strands of DNA."
The article also notes that a study of nearly half a million cell phone users from 1982 thru 1995, did not support an association between the use of cell phones and tumors of the brain or salivary gland, leukemia, or other cancers.
[Edited June 11, 2011 to add information from and reference to the JNCI article.]