Matt Cutts announced at Pubcon on Tuesday that Google have released a tool to disavow links pointing to your website.
This Disavow Tool is aimed at webmasters who have received a notification on "unnatural links".
Following the Panda and Penguin updates this year, many webmasters have received messages in their Webmaster Tools accounts regarding unnatural links and linkspam pointing to their website. This has been Google's fight against anyone building unnatural links to their or their client's websites in order to rank well in Google. It was a common trait of black hat and unknowledgeable SEOs to build low-quality, "spammy" links. And it worked for a while until these updates.
For many, the task over the past few months has been to remove as many of those low quality links as possible before submitting a re-inclusion request in an attempt to get their site back in Google's results pages.
This tool allows for one to submit both domains and individual URLs for Google to ignore. Submissions take place via a spreadsheet shared in Webmaster Tools. Webmasters may modify this said spreadsheet in the future.
Google recommends having a look at the "Links to Your Site" tab in Webmaster Tools. On top of that you may wish to download a full list of your links via Majestic SEO.
You can find the Disavow Tool here: https://www.google.com/webmasters/tools/disavow-links-main, and watch Google's Matt Cutts explain the tool in the 10 minute video below.