I hadn’t heard of this one before but Journalista! linked to tomorrow’s (June 6th) Drawing Day. Charley Parker (creator of the pioneering webcomic Argon Zark and blogger at Lines and Colors) writes:
Drawing Day is an event initiated last year by Mick Gow, creator of the Rate My Drawings site, with the simple intention of drawing attention (if you’ll excuse the expression) to art by encouraging artists worldwide to create 1 million drawings on a single day, and coordinate, cooperate and share the experience through a variety of social networking sites.
Participants can upload and share their drawings, or even draw directly online, through sites like deviantART, YouTube, Red Bubble, Drawspace, Rate My Drawings, Flickr and a number of others. (It’s worth investigating the list of participating sites just to see if some of them are new and of interest to you.)