It's kind of hard to think in just one present, but I'd say that one of the best gifts I received is the collection of many kinds of books that my parents had. They gave it to me once we were doing the spring cleaning of the cellar around 3 years ago. between them are encyclopedias, novels, essays, but one of the most special ones is a spanish conversation guide for german speakers from 1910. The reason I like it the most is because that book belonged to my great granddad who was a german migrant from Hamburg, together with that photo was a photo of his daughter (who was the mom of my grandmom), that's why that book is special for me, because it shows a little part of the history of my family. 

Right now I have the whole collection divided in my whole room, because they are too many! Some of them are in two little bookshelves (the most important or interesting ones) and the rest is in my closet.