You had to got here, didn't you? No really. We are seeing lots of really interesting (free) tools emerging from the mist to help savvy marketers track their meme-contrails in digi-space. A host of them I've used in the past week:
Backtweets.com: Enables you to track WHO has sent a particular URL around, as well as the method folks used (email, IM, twitter, etc.). Great way to see not only what's buzzing but who's buzzing about it.
Tweepz: Lot of folks let you search the content of tweets, Tweepz let's use search Twitter profiles for user's particular predilictions - the only problem being, of course, that the tool will only let you search what they've chosen to make explicit, and yes, Virginia, tastes changes and not everyone reveals everything - still, great as a directional tool and one that lets you rank by #followers, #following, etc.
Bit.ly+: I'm still reeling with this one - grab any bit.ly URL, add a '+' after it and drop it in your browser bar and get all the info behind that link. Given their default position within twitter (and tweetdeck) this is the first of many analytics tools for tracking mini-URL propagation, and giving folks a glimpse into the new frontier of real time idea propagation.