I keep a couple on hand in case one gives me odd results, just to verify.
So in addition to HWMonitor http://www.cpuid.com/hwmonitor.php
There's RealTemp http://www.techpowerup.com/realtemp/
or CoreTemp http://www.alcpu.com/CoreTemp/
or SpeedFan http://www.almico.com/speedfan.php
There's also GPU-Z for the GPU http://www.techpowerup.com/gpuz/
In my experience, and everyone's is different, HWMonitor tends to differ more often from the others. I use RealTemp more often. I've also noticed a bug in CoreTemp - the temps report fine but the multiplier isn't always right. When Turbo kicks in on my i7 860 the multiplier never rises higher than 22. So, like I mentioned already, it's good to have a couple utilities on hand to verify results.