If you're a Google Adwords user, heads up: it's available with audio now. Coming in under the radar, Google Audio Ads has made a softlaunch. If you are already using Adwords, you'll notice a new little "audio ads" tab at the top of your account information.
To stimulate interest, Google is also offering $400 in free advertising to customers who try it out. Not everyone has a speaking voice like James Earl Jones. So they also have professional actors to voice your radio spots for you, as well.