Intel Burn test is pretty much fool proof - if your CPU survives that is.

I'm joking about the surviving part - mostly - since all modern CPU's have thermal check circuits that should shut them off like a light switch if they really do get too hot. But the point is that IBT will stress your chip AND memory to the limit depending on how you set the parameters.

edit: here is a link to a dl from Major Geeks but it is also available elsewhere, just google it.