Bristol University - Brunel Collection: Comprises letter books, sketchbooks, calculation books, documents and drawing instruments of Isambard Kingdom Brunel 1830-1866, certain papers of Isambard Brunel, Jr. and Sir Marc Brunel, and also the letterbooks of Henry Marc Brunel.
Brunel Engine House: Looks at the history of the Brunel Engine House, the Thames Tunnel at Rotherhithe, and the careers of Marc Brunel and Isambard Kingdom Brunel.
Marc Isambard Brunel: Brief biography and portrait.
Sir Marc Isambard Brunel (1769-1849), Civil engineer: List of portraits from the National Portrait Gallery.
Thames Tunnel Shield: Illustrated article showing Brunel's shield design for the Thames tunnel.
Wikipedia: Marc Isambard Brunel: Biography, portrait, related links, and references.