For an Earth Day story at Weather Underground we wrote up a how-to on building terrariums. I thought it might be interesting to track the temp and humidity in the small sealed world.
The tiny station sends it's readings to wunderground.com to view and store the data over wifi. The station is viewable at: http://www.wunderground.com/personal-weather-station/dashboard?ID=KCASANFR459
4/2016 - I just saw the fairly recent BME280 sensor, it can read Pressure/humidity/temp on a single component, and reads faster than the relatively slow DH sensors. I would use that rather than the DH22 just for speed, the extra data point is a solid bonus.