O was asked this question today and I can’t help but feel that the pupil wasn’t happy with the answer. So here I go again.
The Control Unit is a sub part of the processor (along with ALU & Registers). It is responsible for the sequencing, decoding and it also synchronizes the execution of the program instructions.
I did find this video though that covers a range of topics.
[kml_flashembed movie="http://www.youtube.com/v/HEjPop-aK_w" width="425" height="344" allowfullscreen="true" fvars="fs=1" /]
So to sum up, the Control Unit, controls all operations of the CPU, It also controls the flow of data along the buses.