There are several Guitar Centers with the usual stuff. The one on 73rd and Cicero probably has the best bass selection. Lots of used high end stuff- Lakland, MTD (they have the actual one that was on the cover of Bass Player mag), Bolin, LowEnd jazz, and some others I can't think of right now. Plus the usual Spectors, Warwicks, etc. I would recommend that you get to BassClub Chicago. It is in Alsip, IL. It is just outside Chicago at 12213 S. Cicero. It is a small shop that carries a ton of high end gear-lots of Laklands, Sadowsky, Spector, Ken Smith, Fodera, Modulus, Elrick, Eden Aguilar, and more. The owner is a really cool guy that will let you play anything there. Check out their website
www.bassclubchicago.com. There's also Make'n Music but I would not recommend them-very snobby. Another small shop is Musicians Network at 5500 N Clark.