G.T.
Seriously the easiest and most remembered gift that you can give him is some good Christmas sex. Let him be in charge of it all day, sneaking off when you can for quickies, and just love him up, it's the last sex of the year and mine always remembers the details of the year before. It' cost nothing but a little bit of your time, imagination and maybe a cute new red nightie.
I asked my dil what she was getting my son for Christmas and she said he only wanted "her", that's what he told her.
Mine still remembers the red flannel gown I wore last Christmas.
Trust me girls, it works. It's better than buying them something lame.