The present my adult children and their spouses seem to like the most, whether for birthdays or Christmas is a year of paid for AMAZON PRIME! They love it cuz they can get free 2 day priority shipping, stream free movies and tv shows and hundreds of other premium free goodies. So if you are stumped and don't know what will fit and whether they already have one or not...just give them the gift of a year of AMAZON PRIME!
And if the kids are home from college over the holidays...of course they are, where else can they sleep til noon and eat for free??? Give them the gift of AMAZON STUDENT!
Or...if someone comes home and tells you that you are going to be a Grandpa or Grandma...sign them up for the baby registry!