Acurite is the most popular on this website--just do a search for that word and you'll see what I'm talking about. Not made for herps--rather, it's a digital indoor/outdoor thermometer that comes with a hygrometer (humidity gauge). It's inexpensive--around $15--and widely available. Wal-Mart carries them, as does Lowe. Not sure if they're all under the same name brand--it's Acurite at Wal-Mart--but they're easy to spot once you know what you're looking for. I'm sure Home Depot likely does as well. Besides having the ability to measure temps on BOTH sides of the tank, it also makes sure your humidity is right. Don't use the dial types sold by pet stores. I still have my old humidity dial gauge up for laughs more than anything else, and it's horribly inaccurate.