Freeplane - Freeplane is a powerful and free software for building mind maps.
Open Peeps - A hand-drawn illustration library.
vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.
Control Illustrations - 108 free flat illustrations with customizable characters
Pencil Project - Single-user mockup / wireframing / diagramming tool
DrawKit - MIT licensed SVG illustrations, in 2 styles