Oh, I have tons of suggestions--fortunately, I already have a list for when I get this question from friends. It's gonna be cold, so be prepared.
*First of all, good job on setting up the Lakland tour. Great people, and I love the basses. I live about 15 minutes away.
*I normally recommend the John Hancock building over the Sears, because it's right next to the lake and you get cool views of the water and Lakeshore Drive, while still seeing the Loop. BUT, I haven't been to the Sears since they put in that glass balcony thing, and it looks very cool.
*Don't expect too much from Navy Pier. The inside, particularly the front half, is pretty much like a mall. It's worth walking around the outside, though.
*Michigan Avenue north of the Chicago River is shopping galore, if your wife wants to go somewhere else while you go to Lakland.
*If, somehow, it's not too cold to be on a boat, there are some cool tours of the river that also go out on the lake. Wendella's tours leave from a spot below and to the side of the Michigan Ave bridge over the river.
*Millennium Park, which is on Michigan Ave. a couple blocks south of the river--check out the Pritzker Pavilion (beautiful outdoor venue), the Bean (big, reflective sculpture) and--if it's not too cold to run the water--the towers with videos of people's faces on them.
*Next door is the Art Institute of Chicago. They have a great collection.
*Next to Soldier Field on Lakeshore Drive are the Field Museum of Natural History, the Shedd Aquarium and the Adler Planetarium. I've never been to the latter, but the first two are worth the time and admission price, IMO.
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*Gino's East pizza, the main location at 633 N. Wells (this is about 5 blocks north of the Chicago River). Best deep-dish pizza I've ever had, period.
*The theater district is in the north end of the Loop, if you're into that. For more artsy, funky productions, Steppenwolf Theatre is a couple miles away--the Red Line of the El gets you within a couple blocks.
*Second City is also a couple miles away. The shows are generally good to very good. Take the Brown Line from downtown and you'll be 2-3 blocks away.
I'm sure there's more I'm forgetting. Where are you staying?