I would have to say my fav is the one I'm using right now. There would be another silver dragon pic I like more, but it's too busy for an avatar. The short and sweet of this pic is that A) I love fantasy, unicorns, wizards, dragons...that sort of thing. And B) My screen name is also the name of one of my favorite D&D characters I'm currently playing who happens to be a half silver dragon.

I also like the pic I'm using for my profile and have used that as an avatar on other, non animal related sites.