Best trash: Tie between the Bridge of Doom between Jin'Rokh and Horridon and the Sewer of Death before Ji-Kun. Honorable Mention: The Ritualists before Dark Animus
Best boss: For mechanics and design the winner is definitely Dark Animus. For feeling and whatnot? Lei Shen. Honorable Mention: Primordius (love that his room is a Prometheus reference)
Best looking weapon: Greatsword of Frozen Hells for my class. I also like Uroe but the model is too small for most races/classes (exception for TG warriors when and if they can ever use polearms in one hand - then they can be Lei Shen via transmog)
Where it ranks in your top wow raids: I'd say it's realistically my third or fourth favorite. I liked Ulduar more than any raid they've ever put in this game and I think Icecrown Citadel and Black Temple will always be two of my favorites because of the involvement of hugely important story characters. I also give an honorable mention to Karazhan, which is probably tied for third or fourth with ToT.