Google announced on Google+ that they've launched a new ad unit design for their AdSense text and link unit ads. They said the new look is modern and "introduces a minimalist design that brings the focus back on the text content."
Here is a screen shot of the new look for the ad unit:
The new look should be rolling out soon, Google said.
Google also linked to the help document that shows how you can customize the look and design of your ad.
Forum discussion at Google+.
