The Obama administration has started a program called We the People, which is a way for citizens to petition the administration to take action on a range of important issues facing our country. If a petition gets enough support, White House staff will review it, ensure it's sent to the appropriate policy experts, and issue an official response.
The White House website states that if a petition receives 25,000 signatures in the first 30 days then it will be reviewed and a response will be given. At present there are 190 petitions ranging from "Stop All Wild Horse Roundups" to "Save the Postal Service." After scanning through the petitions the one I found that had the highest signatures was titled "Legalize and Regulate Marijuana in a Manner Similar to Alcohol" with over 55,000 signatures.
You can look through them yourself or create your own at https://wwws.whitehouse.gov/petitions#!/petitions