Say what you will, but I love SpeedFan once it's up and running. Granted, the initial 'guess the temp' is frustrating, but after it's all sorted out, I've personally found it to be more accurate with the majority of systems I've used it on. But as Cleric mentioned, BIOS is the best way to get an accurate reading as the CPU runs at full speed, but has zero load, for a 'true' Idle temp.