I just use a thermometer I found at my neighborhood Fred Meyer that I got for like $20 on sale or something. I don't have a sous vide so I don't know the particulars of its accuracy, but when water boils it says 212 on it.

http://www.amazon.com/KitchenAid-Gourmet-Digital-Probe-Thermometer/dp/B005FQ2AO8/ref=sr_1_1?s=kitchen&ie=UTF8&qid=1448851968&sr=1-1&keywords=kitchenaid+thermometer