Come on! I know you are all Sci-Fi geeks at heart. The Free Fandom Project is perfect for you. They have free avatars for the best in Sci-Fi like Dr. Who, Buffy the Vampire Slayer, Torchwood, Harry Potter, Sweeney Todd, Yellow Submarine, Angel, Charmed, Smallville, Rocky Horror, The Shadow, and I, Robot.
Clarification: This is not done by a group of designers but fans who wish to share their love of their favorite items. Give them a break. They are being generous in their own way.
Update: To those being critical of what the Fandom Project stands for, I challenge you to put your talent where you mouth is and design free avatars for the Free Fandom Project.
Free Fandom Project: 10th Doctor Avatar($0L), Angel Avatar($0L), Sweeney Todd Avatar($0L), K-9 Avatar($0L), Dalek($0L)
Total Cost: $0L