I had read in a thread like this years ago that someone would collect a pitcher from each dungeon/cave they were in as a trophy. I thought that was kind of a neat idea. As for me and this run through of the game, I'm collecting one of each perfect gem and putting them in a silver bowl in front of the sitting room fireplace at my home Rosethorn. I have a bowl of keys I no longer need, but can see that I'm going to need at least another bowl for those. I am also collecting the daedec artifacts (the ones I'm not using) but some of them, are a pain to display. For instance, that mace thing sticks through the top of the display case and looks dumb. It also moves all the time - kinda creepy like it's alive or something. It's next to the artifact helm and it moves too. I'm half afraid to move it - it might talk or something. I have saved the robes I received from the mages guild advancements and have them displayed in one of the display cases. I got some special shields for helping various counts and countesses and have them in display cases. I can tell that I will soon run out of display cases.
Thought about collecting books but after spending 20 minutes trying to get 3 books on a bookshelf, I decided that I'll just let that idea go.
Ask for Skyrim, that really depends on how they handle the ability to display and what kinds of items we have in game. If we get special shields, robes or other items for gifts, I would love to be able to proudly display them. I also hope they have lots more display cases or racks in "the big house" assuming there is one. I might try the "trophy" idea for cave crawls, again depending upon space and ability to display. I agree with previous posters that having stuff shoved in chests just isn't quite the same as displaying.