I did it last year for my two and they thought it was really cool.
You tell santa all the details about what each of your kids wants for xmas, their name, upload picture of child etc and then you get the full video to your child via email. It really looks as though santa has recorded it espeically for your child.
You have to be careful the kids don't see you putting in the details and also, if you do it for more than one child, it's best to show them separately as older kids will realise that some of the things he says are identical for everyone.
Easy to make though and looks quite authentic to the kids.