Name some innovative Social Media Campaigns that garner a lot of attention

Beyond the tools, like Twitter and FB, what are some proven strategies or creative concepts that you have seen companies employ to build their brand. For instance, one company I know of, is currently doing a promotion where if people at WholeFoods where stripes, they signal that they are interesting in hooking up. Or the hipster did a post on hacker news that got him 10K sign-ups in 2 days.

So my question is, what examples or just ways of thinking would you offer for how best to start meaningful social media campaigns?

The problem is that once someone else comes up with something anything you do is seen as sort of ripping it off or copying it. The nature of these things is that they are original. The best way to start one of these campaigns is to really understand your audience. What are their behaviors, where do they hang out, what are their interests, etc. Then you need to craft something original and compelling around that.

If you just want some examples of stuff done in the past I would say Old Spice's day of video responses to tweets, Facebook, and Reddit questions garnered a lot of attention.

ARGs (Alternate Reality Games) have done well in the past - last major one I know of was for The Dark Knight.