huKSer,
First let me congratulate you on your fantastic choice to visit the glorious city they call Chicago. IMO, there is not a better place to be in the summer.
A few suggestions:
Willis Tower - I actually work in the Willis (84th floor with a window). There is plenty to see here. The skydeck is a must but I have a better suggestion......The Hancock tower off Michigan Ave probably has better views of the city. You can go to the Signature Room and not pay the $14 bucks to go to the skydeck. The Signature Room is a bar so you can enjoy a nice cocktail and the view or just walk around the bar for free. By the way, the best view in the Signature Room is from the womens bathroom.
Pizza - Most tourist go to Giradano's which is fine. My favorite is Pizano's or Lou Malnatti's. Lou's is kinda like Giradano's but better. Pizano's is Chicago style but the crust is almost like a pie crust....so good!
If you like the beach, make an afternoon out of going to North Ave Beach and Castaway's. Castaway's is a "boat in the beach." Drinks, food, live music (sometimes), etc.
Michigan Ave-Magnificent Mile - a must-do walk for all tourists.
Museums - always a good idea.
Live Music???? If you enjoy live music, check out Kingston Mines. It's a blues bar that has high quality live blues every night. The best stuff comes on after mid-night FYI. I go here all the time.
If you want more ideas, I've got them. Send me a PM and I will help you find whatever.
I hope you have a great time!!