In my opinion Everest is way too complex to use as a temp monitor.
Here are my suggestions.
I like SpeedFan as a temp monitor for two reasons: it displays values close to those of CoreTemp (believed to be very accurate) and it can graph a historic chart of the past 15 mins, which is very useful to observe the temp behavior of your CPU.
CoreTemp is a small, simple and supposedly very accurate app to measure your Core 2 Duo temperature. Keep it on your system tray at all times!
: Super Pi Mod
We all know Super Pi. This version is a small modification that displays times with milliseconds (the normal Super Pi only displayed seconds). It's the same in every other way. The time it takes for it to complete the 1M calculation is a standard benchmark nowadays. Because the time will go down as CPU frequency increases in a very linear fashion, it's very useful to check overclocked performance. Keep in mind, however, that this benchmark is very limited and does not represent the overall performance of your computer.
: Orthos Stress Prime 2004
Orthos Prime 2004 is essentially a moded version of Prime95. Its interface is completely redesigned to focus on CPU torture testing (ie: stability). Choose small, in-place FFTs and run this for a couple of hours to determine if your overclock and temperatures are stable. This app will stress you CPU far beyond the capacities of any regular Windows app. The ultimate stability test is running it for 12 or 24 hours continuously.