For his 60th, my brother and I got my father a fancy chess set of carved figurines (like the crusaders v. Ottomans, or Germans v. the English). It seemed like something that was vaguely commemorative, certainly special, and also lots of fun.
My Uncle turns 50 this year and we decided that a fun gift would be a family tree. I think at this point in a person's life it is nice to look at what legacy they are a part of. Something more personalized like a family coat of arms would be a unique gift also.