Jack McClane (son of John) will be played by Jai Courtney.  If you watched the series Spartacus: Blood and Sand you will recognize him.  If you did not watch it...you should have.  Pull it up on Netflix or something.  He is this guy:

The new Die Hard movie will be called A Good Day to Die Hard.  Stupid title?  Yes.  But I still think it will be awesome.  Here is a picture from this guys screen test with Bruce Willis:

Look for it to hit theatres Feb. 14th of 2013.  Here is a short plot synopsis from 20th Century Fox:

"A Good Day to Die Hard puts McClane on an international stage -- truly a NYC fish out of water in Moscow -- and introduces his estranged son Jack. An apple that has not fallen far from the tree, Jack may even be more of a hardass than his father. Despite their differences, they must work together to keep each other alive -- and the world safe for democracy."