I've been trying to convince my wife's family that I don't want birthday or Christmas presents for years. No such luck... I end up having to put a bunch of useless crap on my amazon wishlist just to keep them happy.
The trick is to request non-physical stuff. As an example, request a track day on a race car track (if you're into cars). That way, you get an interesting experience and no/reduced clutter.
I always ask for Kiva or Watsi gift cards/donations in my name, and make it very clear that any other gifts will get sold or returned to fund those two things.