I'm bringing this back today for the 4th of July: I first saw these floating up in the sky about a year ago and they blew my mind. Silent and luminous, they float upward on the breeze driven only by a small flame in their belly. I saw one after another lift off into the sky and they never seemed to stop. They are more heavenly than earthly.
What are they? Chinese Sky Lanterns are light paper balloons that rise on hot air and then fall when the heat element goes out. Traditional in some Asian cultures, you can read more about them here, but they seem to have caught on in this country in the past few years and we've now got a lot of sources for them, as well as Eco versions that help deal with the fact that they can be messy when they land. The site listed above is the cheapest site I found, but I also found them at Wishlantern.com in what looks like a more premium version, as well as at Amazon.com of course.