I would know she had discovered something she loved when she would forbid me to walk behind her when she was at the keyboard, and I could clearly see that she was in town. She wrapped each gift with care, usually sending it along with a vendor-bought sweet treat if she had enough silver. None of these gifts were remarkable in and of themselves, but they were all so full of her joy of discovery and anticipation of sharing that nothing else I've ever been given can ever match them.
Of course, some players get more substantial gifts. The mount or rare drop that goes to the hard-working GM or guild officer -- that's a pretty commonplace but heartfelt gift. And what about all the players who get married both in-game and out? Their in-game wedding rings often seem almost as meaningful to them as the ones they wear on their hands. Or the practically anonymous leg-up packages that kind high-level players sometimes bequeath on random newbies -- that's sheer awesomesauce right there.
What's the best gift you've ever received in game? Did it commemorate a special occasion? Was it a reward for something you'd done? Was the giver a friend or guildmate, or was it perhaps someone you didn't even know?