This PDF has a lot of interesting information on radioactive substances found in nature. I dug it up while researching the previous item.
The most interesting single fact IMO is this "Sea water contains some 4 500 Mtons U". Next to that, Ted Turner's stash (described in the next item down) is trifling. Hmm....
There's also some interesting but highly technical info about radon gas.
In short, if you're trying to rid your life of radiation, you're living on the wrong planet.