Black, oval, reflective object seen gliding through the daytime sky.

At approximately 8:30 AM on Monday, October 29, 2007 I witnessed a black, oval object in the sky just east of Sioux Falls, SD.  It was quite high and still quite large considering how high in altitude it was. At first glance I thought it was an enormous bird based upon how it seemed to be gliding through the air. However upon further inspection I noticed that it was actually shiny and highly reflective. It moved at a fairly consistent pace, and it moved fairly quickly although slow enough that I was able to run into another room (to get a better view out of our sliding glass door) and it was still there. Again, it seemed to be gliding, but definitely not decending or falling. It went behind the large number trees in our neighborhood, and I was unable to see what happened to it from there.
 Right before it went behind the trees there was a helicopter in the air which passed near it (although the helicopter was quite a bit lower in the air, it passed in the same vicinity...almost right under the object). I didn't get a good look at the helicopter so I don't have a description other than it was definitely dark in color. I was mostly transfixed on the other object. We do get a lot of hospital trauma helicopters flying over our house from time to time as we live on the edge of town, so the helicopter didn't strike me as unusual at the time.
 I am a 30 year old woman and I have never seen anything like this object before in my life.  I have seen large weather balloons gliding high in the sky and I can tell you this looked nothing like a weather balloon. It was jet black with a highly reflective surface. It appeared oval in shape and moved at a medium, consistent speed. I heard no noise from it...although the approaching helicopter could have drowned out any sounds. It was a crystal clear sky, with little to no clouds and no haze or fog. And I no, I had not been drinking. :)