Drawasaurus - Drawasaurus is an online drawing & guessing game you can play with friends or strangers.
iSketch - Isketch is a Free to play, Puzzle, Education, Word, Drawing and Multiplayer video game.
skribbl - Word guessing based on drawing.
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
iSketch.net - A thrilling pictionary online game in various languages.
Drawception - The browser-based party game that combines the telephone game with drawing! Hilarity ensues.