Data Validation with Free Entry, but needs to update Validation List with new value

Of course,

The end result required is a drop down box that allows for free entry. If an item is entered instead of chosen from the drop down box, I need it to add itself to the possible options that can be chosen from the dropdown list.

I used Data validation because I know that I can create a drop down box using that without having to go into ActiveX or Form controls. I have turned off the error function of data validation to allow for free entry.

If there is an easier way that I am unaware of, I am happy to use it.