I have an "Impossible To Buy For" (ITBF) DP.
There's just nothing he's particularly 'into' and he's pretty happy with the simple things in life.
We don't do 'big' presents for each other so that makes things easier but I still find myself wondering what on earth to get every year!
Added to my DP's pre-existing ITBF-ness, my mother insists that I buy all of her presents to DP as well. And, as if that's not enough it's also my DP's birthday a week before Christmas.
So, DP's ITBF-ness is tripled because I have to buy Christmas presents from me, Christmas presents from my mother, and birthday presents.
We don't do 'big' birthdays though so a few little things are okay.
I usually get DP a jumper or a hoody of some kind, a few bottles of expensive/unusual booze, and a few books as standard.
I also tend to get him a few bits and pieces for his office which would be a horrible, soulless white box if it wasn't for my flourishes 
I've bought him a fancy advent calendar but that's not really a Christmas present as such.
At the moment, DP is developing a small hole in his jeans and I'm excited because it means I have another present idea - NEW JEANS 
Ladies with ITBF DP's.... tell me your tales of woe, and let's share some ideas!