"I've been using SpeedFan for a very long time to accomplish just this, because my computer fans are not too great. SpeedFan provides very many options and shows you all the core and ambient temperatures that are measurable for your computer. I really recommend it. The interface is also quite simple, and getting it up and running is easy!
By the way, SpeedFan also allows you to change clock options for your motherboard, as well as many other things. It has a very cool graphing option now, which you MUST check out! ;)"
Core Temp: Fast, free, and accurate. It comes in 32-bit and 64-bit builds. I use it on both my servers to monitor temperatures. You can also have it log temperatures so you can graph out trends in a spreadsheet.
