You could cut some frames out (which will make it faster though) and reduce the amount of colors you've got in it.
Really the 100KB limit is pretty low so you're going to have to make a lot of sacrifices if you want long or complex avatars.
It's free and it's working good !!!!!
http://www.online-image-editor.com/
proof: downloaded dimensions: 500x500: http://imageshack.us/photo/my-images/706/iaf.gif/
make it trough online program 100x100: http://imageshack.us/photo/my-images/547/l97.gif/
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ENJOY !!!!!
I have done this: http://gifs.gifbin.com/052009/1243329491_animated-andy-gilmore-art.gif
to this: http://imageshack.us/photo/my-images/11/pt7l.gif/
OK, it looks not so good as the original, but not that worse as the OP (no offense please !!!!!)
How do you resize gifs? I was about to make a topic asking this but I figured I may as well ask here. Can you shrink the image or do you need to cut it. If so, how?