To me it looks like either Araneus diadematus, which is a european garden spider that can be found in the US

http://upload.wikimedia.org/wikipedi...5-08-18_02.jpg

Or some type of Orb Weaver (family Araneidae) (There are tons of orbs that vary in look so I don't have time to try to find the closest one it looks like, but if you look at the image search below there are a couple that look like your spider)

http://images.google.com/images?hl=e...-8&sa=N&tab=wi

http://www.mkgray.com:8000/pix/orbweaver-spider.JPG

I see similarities with both but I'm just doing this before school so I don't have a ton of time to look