Hi, J.!
I recently had the same problem... it is hard to know what to look for. I used iParenting's preschool/day care checklist to compare three places in the Oak Lawn/ Beverly area. The checklist is on the iParenting website, I think, but I found it by searching "Day care checklist" on Google.
I recently enrolled my daughter in Penny Lane School. She starts on Monday. It is on Southwest Highway in Oak Lawn. We have taken our little one there several times for a visit/tour and she loves it. There is an open house tomorrow from 10-12 (I think). They have a website: www.pennylaneschool.com. My husband and I like it... for what it is worth.
Good luck!
E.