The RT8100 Fridge/Freezer Thermometer from ThermoWorks makers of the nearly universally lauded Thermapen. This thermometer displays two temperatures via and LED display. It has programmable out-of-limits alarms and a magnetic back. Also has the ability to show min and max temps.
You could use this to monitor your kegerator, fermentation chamber or If your fermentation chamber and kegerator are close, you could monitor both with this unit. The min/max function is handy for getting a general idea of how well your kegerator or fermentation chamber is performing.
As of this posting ThermoWorks has the RT8100 marked down from $29 to $22. Check Thermoworks for up to the minute price and availability.