Open Peeps - A hand-drawn illustration library.
skribbl - Word guessing based on drawing.
Control Illustrations - 108 free flat illustrations with customizable characters
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
Craftwork - A collection of User Interface resources made by Craftwork
gartic.io - Draw, guess, and win!