It's typical if not expected for users to upload their own avatar. You're certainly welcome to, and encouraged to personalize your own profile the way you wish.
But for those of you who who want content relevant avatars, I made a few in Photoshop for your use. When updating your profile and asked to select which avatar you would like, these can be found under "Forum Avatars".
"From void evolved Phyrexia. Great Yawgmoth, Father of Machines, saw its perfection. Thus the Grand Evolution began." ~ Phyrexian Scriptures