Wired today offered some advice on how to safely leak information to the press using a "burner phone", computer or tablet.
Get a dedicated computer or tablet: the cheapest Windows laptop will do. And pay cash... Leave your cellphone, your normal computer, and your metro card (like SmarTrip) at home: anything that speaks over a wireless link must stay behind. Then go to a coffee shop that has open Wi-Fi, and once there open a new Gmail account that you will only use to contact the press and only from the dedicated computer. When registering, use no personal information that can identify you or your new account: no phone numbers, no names.
...When you are done you must clear the browser’s cookies and turn off the Wi-Fi before turning off the computer and removing the battery. The dedicated computer should never be used on the network except when checking your press-contact account and only from open Wi-Fi connections away from home and work.