I will go modern with this, my favorite item, more than any sports item I have. Complete main cast and crew signed Empire Strikes Back Poster. I know of 4 others like this, 2 of them owned by Steve Grad, but none on this poster type.
Movie had such an impact on me and putting the poster took so much time (over 15 years traveling to two continents) and money (I have a picture of Ford signing this poster). All that being said, many times I have thought about selling/trading as it doesn't really fit my collection.