The Mendota Bridge, and Mounds Park are probably the most picturesque views you'll get with both downtowns included. Another cool spot I remember is on top of the old Hamms brewery but I'm not sure if it's even possible nowadays.
From a plane however this recent picture has to be one of my favorites.
twins (http://www.flickr.com/photos/punchup/6216197984/ - broken link) by
Punchup (http://www.flickr.com/people/punchup/ - broken link), on Flickr