Besides the ones already mentioned, two trades I think of both involve Ricky Davis.
First Danny traded 2 fan favorites in Eric Williams and Tony Battie for Ricky Davis. To me that would have been like trading Jae Crowder and Amir Johnson for Nick Young. Two guys that played hard and provided veteran leadership for one of the NBA's biggest knuckleheads.
But then I actually fell in love with Ricky, because Ricky actually played hard too. I believe Doc once said Ricky would run through a brick wall for him if he asked him too. Plus he had a lot of charisma and appeared active in the community, bought a whole section of season tickets for fans, etc. He was still part knucklehead, but he was our knucklehead and had a heart of gold. Then he was traded for a similarly productive player in Wally, without any of the charisma and who didn't appear to play as hard. It was like trading Jae Crowder for a prime Jeff Green.
I was disappointed when Danny traded for Ricky, then I was disappointed when he traded away Ricky.