CPULoad for Mac

From Lobotomo Software:

You don't need to be a geek to wonder what your CPU is doing all day long! Sometimes applications (not ours, of course) go astray and hog up CPU cycles, nicking them from other applications and winding down your productivity. CPULoad offers a simple and light-weight possibility to have the state of your CPU readily available in your menu bar.

If the load of your CPU looks suspiciously high, have a closer look at what is causing the load by launching Apple's Activity Monitor with a single mouse click. Activity Monitor lets you look at the process details and you may terminate the rogue process if required.