Custom avatars are a great way to get the face of your personality on the web. With an avatar, you can be as sexy or concervative as you want to be. Your avatar doesn't necessairly have to look like you, but it's kinda fun to give her some physical traits that resemble your "real" self. :) They also make really cool swag give aways at cons and reader signings. Bookmarks or postcards with your book or website information on one side, your author bio with avatar on the other are always impressive.
For my avatar, her hair is what we have in comon. Hair and eyes.
Consider adopting an avatar for long term use. Your readers will love it, and you're be a highly visible, easily recognizable presence in the virtual world.