CPU Grab Ex is a tiny portable tool which can consume a defined amount of your processor power. This could help you monitor CPU cooling, or test the effectiveness of CPU optimisation software (resource hogs should see their CPU priority drop).
The program launches as a simple system monitor, displaying the CPU model, speed, and the current usage of every CPU core.
Use the slider to set the percentage CPU usage to consume, click the "Grab" button and watch as each CPU core gets busier.
There's also an option to grab GPU power, although this only works if you've an OpenCL-compatible graphics card.
Beware: allowing CPU Grab Ex to use a high proportion of CPU power could bring your system to its knees, maybe even cause a crash in extreme situations. Use the program with care.