Dont know if using grafical LCD is very effective way of building thermometer, but if you have few spare laying on your desk – why not. As a result you can bild very cool thermometer as Andrei did.
He used few standard parts like PIC16F88 microcontroller, KS0108 graphical LCD and couple LM35 temperature sensors.
He also made Proteus VSM simulation – this is much easier to test firmware or even modify existing one without building real board. All necesasry files including source code written for CCS C compiler, Proteus VSM simulation file and hex you can find here.