andrew
everything you'll want to see is literally in a 3x8 block area.
Start at Randolph & State. You will be able to see the famous Chicago theatre sign. Then proceed east on Randolph until you get to Michigan Ave. Millenium Park (with the Bean) is right there. Then just take Michigan Ave. north. All the interesting architecture/scenery is there - the Chicago River, the clock tower (not sure what it's actual name is), the Water Tower, Hancock observatory, the medieval looking church. It is also the best street for shopping, esp. at the Water Tower mall. If you want to see the city from above, go to the Hancock not the Sears Tower. It's closer, and it has a better view of the lakeshore.
Rush St. is the best place for car spottings. Just hang around Bentley Gold Coast, and you'll see both the dealer cars and random cars driving by. For dinner go to Giordano's at Rush & Superior. Best deep dish pizza in the world. Also, when you're done looking at everything else, take a walk along Lakeshore Dr, very nice place to walk with the busy street on one side and the beach on the other.
I don't recommend the Sears Tower or Navy Pier. Navy Pier probably isn't fun by yourself, and the Sears Tower isnt' as good as the Hancock Observatory. Hope this helps
Made a map for you (actually used it for my own trip)
http://maps.google.com/maps/ms?hl=en&safe=off&client=firefox-a&ie=UTF8&msa=0&ll=41.892311,-87.624035&spn=0.030285,0.063&z=14&msid=117880911069672026950.000458a1bd43c38c81fcb
