Well, could be a lot of things. Anything that speedfan can pick up that has a sensor, it will report on. But the information regarding the sensor is provided by the device itself, not determined by speedfan.
One of them is likely motherboard temperature at the northbridge. The others could be mobo related too, or could be a PCI device that has a sensor. The fact that you have a core temp but not a cpu temp means that one of them could be cpu. Another is likely the gpu. So it's possible that you have temp 1, 2, and 3 as cpu, northbridge, gpu. Not necessarily in that order either.
You might want to look when speedfan initializes and find the address it's reporting the sensor on, then go through your device manager and look at the device information and try to match the address with what speedfan is looking at. A bit tedious, but otherwise I won't know for sure.
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