To do:  
-Museum of Science and Industry (Some good aviation stuff)
-Field Museum (One of the best 'regular' museums in the country)
-Shedd Aquiarium (Second only to Baltimore's)
-Adler Planetarium (Awesome if youre into astronomy)
-Wrigley Field (No brainer)
-Soldier Field (Im not sure what the construction altered about the building, but it used to be a very unique stadium - had more in common with a castle than a football field - its also right next to all the museums)
(Nightlife has been covered)
Food:
-Portillos (Best hot dogs in the nation - but unless you put everything on it, dont even bother.  Also try their 'beef' that -Funked was speaking of - Portillos does it best.  A 'beef' is kinda like a Philly cheese steak, but the meat is cooked differently and there is no cheese.  FIgure out what you want ahead of time or they start screaming at you - its fun)  
-Mortons (Duh)
-Billy Goat (Tavern - 'Cubs curse.')
PS:  Chicago food is very onion and mustard/horseradish heavy - its a taste that isnt quite duplicated anywhere else.  The food is fantastic - everything from a sub/hoagie/hero to exotic dishes has its own unique 'Chicago' taste.
PPS:  When/if you order soda, dont be confused when your server asks you 'what kind of Coke do you want?'  Coke = soda, so its perfectly acceptable to answer her question with 'Sprite.'  

Hotels:
Plenty around Ohare and you can take the El anywhere you want to go.  The marathon is over so finding a room shouldnt be difficult at all.
Have fun - its a great town.