5. Uranium Ore
Why own a Geiger counter if you don’t have something to test with? A company called “Images SI Inc.” is selling a chunk of uranium ore for educational purpose only. With its low radioactivity, it should be relatively safe to use by anyone, as long as they are sensible enough to use a glove when handling it. You can get it now for less than $50.
http://www.amazon.com/gp/product/B000796XXM