A. Linkable items in chat
It's a familiar concept to anyone who has played WoW (or, I imagine, several other MMOs) - Just shift-click an item that's in your inventory, and a clickable link is pasted into chat that other people can hover over and see the item's specs and appearance. Also, alt-clicking to preview the item on you.

B. Outfit design web-page
Let's face it, this game is 60-80% dress-up. It would be extremely useful to have some kind of page that allowed you to assemble an outfit with all of the available items and modifiers in the game - allowing you to see exactly what you would look like, and what items you need to get that look! Currently, you're limited to what's in your inventory and what's on the AH - that doesn't necessarily allow you to preview the full look.

On top of that, you could use that page to save outfits and create "wish lists" so you don't forget what you're looking for. Boom. Suddenly, everyone has a look they're going for, more accessories are needed, more keys are needed, more CE is used, more CE is purchased. Just sayin'.