Serverside faces and decals would be nice, so that you can have a set that fits the theme of a server. Default generic faces/decals for avatars would be nice, though.
Maybe an option to set a server-specific avatar, so you join one server and you use your usual avatar, but if you join a server that you've set an avatar for it spawns you with that one instead?
...or just let us have more than 10 favorites. Just throwing ideas out there.