[CentOS] Process run away

Hi,

I just found that one of my centos servers was running at 100% cpu and 
had used up all the memory.

I checked system monitor and was not able to find the culprit,  I 
restarted the server and it seems fine now.

Does anyone know of a simple way to have the server email me if the cpu 
load is at max for x amount of time.  I am not
sure how long it was running like that, I have not checked it for a while.

What would you recommend for something like this

Thanks

Mace