I use a Springfield Precise Temp that I got from Home Depot for $14.99. It displays temp/humidity or temp/time. I would not reccomend getting this one however.
The humidity gage is extremly inaccurate. It does not go above 39%. You can submerse the darn thing in water (Ive tried) for 15 minutes and it will not go above 39%.
My friend had hers in her incubator and it displayed 29% and never anything above. (Which is total bull...)