Product review (4 stars): Great Frige Thermometer (Includes secret formula for C to F)
This is a great product for the price.  It would be nice if it had a Fahrenheit switch though.  I know others have messed with the circuit board to get it to show Fahrenheit, but I found a secret formula to convert C to F:  F = C * (9/5) + 32.  I have attached a table that you can pin to your refrigerator.