What Tony said is fairly reliable. Navy Pier... it's a bit too gentrified and artificial to me.
The South Loop can offer some interesting choices, but then, if you're after street shots, go for the area around the Art Institute, which is Millenium Park. That spot, however, gets old pretty quickly, so head North via Michigan Boulevard or Avenue all the way to the Water Tower, which may offer some nice opportunities.
As for urban scapes... you'll find them along the Michigan Blvd as well. Some are in the Chicago River area, around the bridge by the Wrigley building and the Chicago Tribune tower. Before the construction of the Trump Tower there used to be a nice spot near the bridge that offered a nice view of the buildings along the river. There may be something left, but I cannot recall.
Check my M4-2 blog for ideas about street scapes and shots in Chicago. I've posted a few... from years ago. They're in entries from late last year.
Take care!