NASA is set to launch the billion dollar space probe Juno today. It is destined for a long voyage to Jupiter where it will enter orbit to study the planet and its moons in more detail then previous missions such as Galileo. The journey will take six years and will include flybys of Mars and Earth to send it further out to the gas giant.
If all goes well the rocket will be sent into space on an ATLAS rocket in the next few minutes (12:25 local time). You can watch it on NASA TV.
Update: The launch was a success. Here is a recording in case you missed it.