Like they said, definately visit the Shedd. They have the "Amazon Rising" exhibit with some moster pimas, rays, aros, etc. It's pretty cool. Also, if you have never been there, I think the 'Oceanarium' (the area with the dolphins and whales and stuff) is worth the extra money to get in to.
As far as LFS's go, I'd say check out the Living Sea Aquarium in Park Ridge. They are sort of expensive, but have a nice selection and some huge display tanks/ponds with blacktip sharks, tarpon, rays, etc.
Also, it just opened recently, but Aquarium Adventure (
http://www.aquariumadventure.com/stores/illinois_hoffmanestates/illinois_hoffmanestates.htm) is pretty cool - biggest selection of freshwater fish that I've found in the area.
If you're here 6-30 trough 7-2, are baseball/Chicago fans, and can get tickets, I'd say definately try to make it to a Sox vs Cubs game. That'd be a good way to break your bro in to Chi. Maybe you'll even see a brawl again lol. Wrigleyville's got some bars to hit up afterwords too.
Let me know if you want to know anything else.
