I have not set my avatar, so is there any recommended web application for creating an avatar? (If the app can import photos, that will be nice)
Go to your user page and edit your picture, it will redirect you to Gravatar , easy and useful to associate your avatar with your email address.
Really, any standard image can be used as avatar.
But I know only one website dedicated to avatar creation : Eightbit.me is a service to help people create 8-bit avatars.