Both RC helicopters and DSLRs have shown some amazing advances and when they're combined the results are amazing. Eric Austin has a company called Heli Video that specializes in this with a helicopter-mounted Canon 7D and the footage rocks. With a free-roaming helicopter he can get shots that swoop in and out and then look down from above without any need for a crane or anything else. There are also no mistakes allowed as a crash means several thousand dollars worth of gear get wrecked.
Check out the first video to see what this technique can do and the second for a view of the helicopter at work.