There's a subreddit called "progether" ("programming together") that tries to organize people for collaborating on a series of small projects and coming up with new ideas together: http://www.reddit.com/r/progether/ + http://www.reddit.com/r/progether/wiki/about

It doesn't seem wildly successful, but it's a nice effort, and I heard about it via a computer science student who found it interesting to participate in.