During the lunch keynote in Las Vegas at Pubcon 2012 Matt Cutts, Chief SPAM Engineer at Google announced the Disavow Links tool to Webmaster Tools. I managed to grab half of the presentation in an audio format, which can be listened to at the bottom of this post.
The tool is now live in Webmaster Tools and can be found (once logged in) here at the Disavow Links tool. Matt also added that if you are doing a link reconsideration request due to a Bad Link email recently (since spring 2012), then you should do the reconsideration request first, then start your link disavow in Webmaster Tools.
Much like the release of Penguin, the new Disavow Links tool is just another step Google is taking to put a heavier weight on the quality of backlinks versus the quantity of links.
Happy link sculpting!