I'm from NY too and I posted a similar thread in OT several months back. I only spent 3 days there, but I had a great time. I got a Chicago CityPass and hit up all the touristy points. I went to the Shedd Aquarium, Planetarium, Field Museum, Sears Tower, Hancock building, Millennium Park, Navy Piers, boat tour, jazz club, pizza and hot dog.
- Pizza - If you've never had Chicago-style deep dish pizza, give it a shot. Lou Malnati is a famous chain, but I went Giordano's (also good) because it was close by. There is a Chicago vs. NY pizza debate. You can decide for yourself.
- Hot Dog - Taste a Chicago dog... basically a hot dog that's nearly turned into a sandwich.
- Jazz Club - I went to Andy's Jazz Club. Nice, cozy place if you are into that stuff. NY has a few jazz clubs of it's own, so I wouldn't say it's very different.
- boat tour - I took the architecture tour from Navy Piers. I thought it would be boring, but I thought it was very enjoyable.
- Millennium Park - I downloaded the MP3 tour from its website, which made it much more enjoyable than just walking around and staring at objects.
- Shedd Aquarium (CityPass) - Nice, big aquarium. NYC's aquarium isn't as nice, so it might be worthwhile.
- Adler Planetarium (CityPass) - This was ok. NYC has AMNH/Planetarium, which I'd say is better.
- Field Museum (CityPass) - Again, NYC has plenty of museums, so this may not be that impressive.
- Sears Tower (CityPass) - If you get the CityPass, it'll give you the option to use it on the Sears Tower or Hancock Building. Use it for the Sears tower. I went at night, which looks amazing.
- Hancock Building (CityPass) - I didn't use the CityPass for this. They have a buffet lunch in the building that costs only a bit more than the price of the view alone. Go for the lunch (if you can) and get the view for free.