I really enjoy when people truly portray their characters through their reactions and thought processes. Though saying words and saying what you're character is doing is basic, it really shows a lot of investment when you allow your character to have an internal process. A lot of people don't understand that "we" as Role Players can only see and understand what another player allows us to see. When Role Playing I look to RP with people that challenge me to express more through my reactions and that leaves it open to many possibilities. I'm sure I could explain this better but bottom line is that its awesome to see a character inside and out and kudos to those who put it all out on the table.

Another thing:

Images. I don't do it. But I enjoy when people supply images of their shoes, clothing, or objects with a hyperlinks. It adds to imagery and fills in the blanks. People around you can definitely understand the image of a character when one supplies detailed descriptions and a picture.