the upcoming con thread if you're interested in details).
Anyhoo, getting back to the subject at hand, I've done my own versions of the "Jillian writing her report" avatar at 117x117 (wide and closeup). I've lightened and desaturated the background somewhat, and slightly lightened the shadowing of Jillians face, to bring out the details and (IMO) make the image work a bit better in an avatar (non)context.
I saved both GIF and PNG versions, though in this case the color compression of the former doesn't seem to created any noticeable effects (perhaps it helped to use Paint Shop Pro's relatively smart color-depth reduction tool before saving). The PNGs are about 20 KB; the GIFs are about 9 KB:
(Edit: "Jillian Writing" avatars included in the larger collection I posted further down the thread. I've also discovered that a good optimized-palette reduction to 256 colors has negligible effect on the appearance of the image at icon size, and got the PNG file sized down to the same range as the GIFs.)
Ditto Scientivore's request: if you want to use them, please host your own copies and give proper credit for the original artwork.