My favorite is the whip of fire and ice and the nightmare sash. The reason is that I love elemental things and dark fantasy things so it made for one of the better combos and makes your avi look amazing. I just pure love them.
My favorite august monthly collectable would be lusty scoundrel, one because there is no other item like it, and two because it has a romantic feel to it<3 sadly since there is no other item like it alot of people want it and it gets overused.
The Nitemare scarf because I think of it as being "true black" because the shading of it matches any other black items on gaia (although most of the black items don't match each other unless they come in a set together).