You're often just two degrees of separation away from the best sources of information. Work your networks and you'll be amazed at who you know. Get their phone numbers through the alumni directory. Chances are they'll be candid with you. Don't just look at where people work.
Organizations convey something about themselves in their selection of frontline staff.
Companies with strong cultures stand out from the moment you walk onto the premises. Look for heroes, listen for stories. Every company has heroes, people who embody the core values. The stories that people inside a company share tell you a lot about the company itself.