Doodle or Die - It's like the game of Telephone. Except with doodles.
gartic.io - Draw, guess, and win!
Drawception - The browser-based party game that combines the telephone game with drawing! Hilarity ensues.
Drawasaurus - Drawasaurus is an online drawing & guessing game you can play with friends or strangers.
LetsDraw.It - Guess and Draw, Drawing Battle, Pictionary, Copy picture - online drawing games where you can compare your skill with others.
Drawesome.uy - Offers both Drawing & Guessing games as well as collaborative drawing lobbies.