For some reason I never seem to have enough long coats in the winter for my avatars. Especially (faux) fur-lined coats are elegant and simple, but so hard to come by. They work well for casual avatars as well as military or historical.
Muted colors are also easier to work with in my opinion, especially with a winter or autumn theme.
Here is an example of what I would like to see more of:
(I only pixeled the male avatar, but it would of course be unisex)
Best of all (in my opinion) would be a combination of more winter hats and coats, like the ones I suggest in my More Themed Hats petition: