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
Although it's Dean that Anna had more of a connection with in the end, she showed a lot of faith in Sam right away despite having heard what the angels were saying about him. I personally feel it's the little moments like her asking Sam specifically if she could contact her parents that show how she understood that he's a good person and trusted him.

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.

Ruby
For all the time they spent together, Ruby and Anna didn't interact with each other all that much. Ruby's involvement with Anna was more a result of her involvement with the Winchesters. She was the one who originally told Sam and Dean about Anna and where to find her. Sure, Ruby did help Anna escape from Alastair when he first came after her and took her somewhere hide, but as soon as she realized Anna was an angel she wanted nothing to do with her. Not only did Ruby say it outright, but from that point on she just never looked comfortable around Anna. It was really only her loyalty to Sam that kept her from running.

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.

Uriel
Uriel, like Castiel, was stationed together on Earth under Anna's command so they may have been close in the past - perhaps even the angelic equivalent of friends. But that was then, and when Uriel was sent to kill Anna in her human form he certainly didn't display any affection for her whatsoever. Rather, he was quite merciless in his pursuit and almost seemed to be enjoying himself. He also kept her grace in a vial around his neck, which really doesn't make sense to me aside from furthering the plot, but then again knowing Uriel's personality he could have wanted to hold onto it for the power it gave him over her. (Whatever the reason, it turned out to be a dumb move as she managed to snatch it away from him and regain her angelic mojo.)

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.