Here's a PIC based temperature data logger. The PIC used is 8-pin PIC12F683 and the temperature sensor used is DS1820 that doesn't require calibration and provides temperature value in digital format. This temperature logger records data inside the internal EEPROM. Each temperature value is 8 byte, so the resolution is 1 degree C.
Besides, the sampling interval is user selectable (1 sec, 1 min, or 10 min). The recorded values can be sent to a PC through a serial port.