Thermistor and Voltage Divider to ADC
Thermisters are generally used for rough measurements around a narrow operating temperature. If you are willing to build an OP-AMP circuit why not just purchase an MCP9700? This is a nice linear temperature sensor in a TO-92 (or SMT) package which is pre-calibrated and outputs a temperature proportional to the voltage. For example .82V = 82degF.