seems like you're using it inside brooder since you tell us "What kind of themometer can I use for the chicks......"
the aim why you're using thermometer is of course to get know temp inside brooder (or temp chick feel) in order to make them feel *comfort* (well, you'll never know how temp will exactly make them comfort except you're the chicks).
I myself have care for chicks for several times, they all grown up well (but finally death of disease outside). I don't use any thermometer for them, I just let my hand inside brooder for couple minutes, feel warm enough, get the chicks in, check for some hours if they feel comfort/not (you'll know but not exactly about their comfort when you heard noisy sound of them). that's all I done when I cared for my chicks.
beg your pardon since my answer didn't tell exact thermometer it won't fulfill your need to know what thermometer you can use. I just tell you my experience when dealing with that cute fluffy little chicks.
For brooding chicks... I have never needed to use a thermometer. I go by what the chicks are doing. If they are all huddled together in a tight buncle under the light, and chirping loudly they are uncomfortable. If they were not under the light, and huddled at the edges of the brooder chirping very loudly, they were uncomfortable. If they were milling about the brooder chirping softly, and playing they were just fine at whatever temp the brooder was at. However, I did put a thermometer in to see what the temp was a few times. Never once was it at 90 degrees the first week. It was more like 80 degrees, maybe 85 for first week. I'd rotate the light at the end of each week to bring the heat down as they got bigger.
For incubating...You can get thermometers a few different places, but some are accurate, and some aren't. Walmart sells an acu rite one that is ok for thermometer, but not so good for humidity. There's a honeywell brand you can get also. It's ok too. Another place you can look is at a pet store that sells reptile equipment. They sell thermometer, and humidity guages. Some are made by flukers, and are accurate. For a hygrometer, you can go to a cigar smoke shop. They have some very accurate hygrometers ( both digital and analog) you will be able to callibrate both.
Either way, for incubating, get to or three different thermometers/hygrometers. So you can run an average. Do a test run before you stick any bought eggs in, and you'll get a better idea of what is accurate and what isn't.