This Nationwide Insurance TV spot, featuring Danica Patrick and Dale Earnhardt Jr.,includes a very clever call-to-action.
Dale pulls a prank on Danica and reveals "her" cellphone number in the ad. But if you actually call the number, you get a message from Danica reminding you to visit the website, and asks fans to leave a message on how to get Dale back. Which, even if not turned into a new ad, it's still pretty engaging.
A bit more engaging and clever than a similar tactic employed by Little Ceasar's spot here.