menu bar to show how hard the processor is working

i've heard some people are using a thing in their menu bar to show how hard thir processor is working. what is it called? and even better, could you give me a link to where i can download it?

Thanks heaps

I use iStat menus.

MenuMeters, turn on the CPU part.
http://www.macupdate.com/info.php/id/10451/menumeters

Another vote for MenuMeters. It is wonderful, and it will show you a lot more than just the CPU if you are interested. For example, you can display your internet traffic, your RAM usage... LOTS of stuff. All of it is updated in real time. I wouldn't run a Mac without it any more.

I previously used MenuMeters, but I have since moved over to iStat Menus, which I find to have a lot more features.