This site by the Library of Congress is a digital exhibit of a scrapbook Carroll kept as an adult. You can look at reproductions of the pages. There is also helpful biographical information about Carroll's life.
"The common ground on which this association ... is founded is the hypothesis that Lewis Carroll was 'simply' a man," writes The Association for New Lewis Carroll Studies. "Not the 'Repressed Paedophile', or the 'Tragic Deviant with the Heart of Gold'... not the 'Social Hermit', not the 'Unfathomable Genius'." This site offers interesting essays on this enigmatic and often misunderstood genius.
This London-based society is made up of serious Carroll fans and scholars. Their site contains useful background information on Carroll's life, such as his family tree and an annotated bibliography of his works.
This is the companion site to the book In the Shadow of the Dreamchild by Karoline Leach. Leach argues that Carroll has been falsely and unfairly painted as a pedophile by generations of readers who don't understand Victorian portrayals of children. It links to interesting documents that shed new light on Carroll's biography.
This is the web companion to an exhibit at the University of Texas celebrating Carroll's 100th birthday. It has interesting pictures and documents from different phases in Carroll's life, from his childhood to his years at Oxford.
This great site about the Victorian era explains Carroll's times. It helps explain the social, political and literary context of his life and work. Understanding the era is key to understanding this unusual artist.