I picked up one of those little battery operated digital clock/thermometers at my local Auto Zone for about $10.
A bigger pic can be seen
HERE
I have it mounted accross the handlebar clamps on my ZN using the 2 velcro strips that it came with, and it holds really solid regardless of how bumpy the road is.
It's designed to be used in an auto and has a 3-position switch that changes the display to show interior and exterior temps as well as the time. It has a small sensor attached to a 6' wire to be used for the exterior temp, and I have that velcro'd to the back of my headlight housing out of view.
Judging by the thermometer display at the bank near my house, and is accurate to within about 1~2 degrees.
The button on the left activates the backlight so it can be viewed at night and stays on for about 3~4 seconds, which is just enough time to see the info.
Sitting in direct sunlight and at higher temps (85+) it causes the face to temporarily go blank. But once it cool down it works fine again.
It is absolutely NOT weatherproof however, and will get a slight amount of moisture on the inner screen if left sitting outside when it's either raining, or when it's cold enough to leave dew on an auto windshield.
The moisture eventually evaporates, and has yet to keep it from functioning.
Overall, I'd say not to bad of a product for a mere $10.