I could run through anyone and everyone Anna ever interacted with, but really there are only three others I feel need mentioning. All were important in Anna's life but none warrant as much discussion as Castiel or Dean. So they get clumped together!
Sam was also always the one to rush Anna to safety or put himself between her and danger. Even when Castiel and Uriel come to carry out her death sentence he stood in front of her despite the futility of the action. (In fact, Julie McNiven, the actress who plans Anna, stated in an interview that she thinks Sam is actually more protective of Anna than Dean is.)
The big difference between the two brothers, however, was that Sam and Anna could never really have had a moment like she had with Dean. Unlike Dean, Sam wasn't looking for someone he could turn to and ease his troubles. He wasn't even close to ready to admit what he was doing and besides, he had Ruby and whatever it was they had going on.
And in the end, whatever connection they shared wasn't enough to keep Anna from trying to kill Sam when she found out he was Lucifer's vessel and his death might save all of creation.
It's a bit sad, because after Anna got over her initial shock upon seeing Ruby - what with being able to see Ruby's true demonic face and all - she really seemed to like her. But once Anna regained her grace they never crossed paths again and I'm sure by then neither minded.
I'm just going to put this out there, but I think a lot of the contempt that Uriel felt for Anna may have stemmed from the fact that she chose to become that which he despised. Uriel never once made it a secret how he feels about "mud monkeys" and although he was no stranger to disobedience, falling down to Earth was something he would never even consider. His sins against God were carried out in order to destroy all humans, not to join them.
The fact that Anna later killed Uriel also put a damper on their relationship.