The Parrot A.R. Drone can be launched and controlled with your iPhone or iPad:
The Parrot A.R. Drone costs $299.
The Parrot A.R. Drone can maintain stable flight at an altitude of up to 20 feet, and a maximum altitude of up to 160 feet.
More sophisticated drones can fly higher and for longer, in a more stable fashion.
For example, protesters in Warsaw used a spy drone last month to see what police were doing. As diydrones.com notes:
People tend to assume that UAVs will be used by the police to keep watch on us, but as ... video, taken by a RoboKopter of riots in Warsaw, shows, they can equally be used by citizens to keep tabs on the police. No need to wait for the local news to send a helicopter to get the aerial scene of a demonstration, just Do It Yourself!
Here is the video of the police shot by the Polish protesters:
(Here's what the RoboKopter drone used by the Polish protesters looks like.)
Drones can range from simple:
To advanced:
For more amazing technology, see this and this.
For information on building your own drone, start here.
Disclaimer: We don't know whether there are any Department of Homeland Security, FAA or other regulations or laws prohibiting flying your own spy drone. Consult with a representative of all appropriate Federal, state, county and local agencies to determine whether or not you may fly your own drone.