I came across an article on the Simply Hired Blog that gives a good Company Research 101 break down.
http://blog.simplyhired.com/2011/07/research-is-key-7-questions-to-answer-before-applying-to-any-company.html?utm_source=newsletter&utm_medium=email&utm_campaign=jul12
In addition, I believe that the MOST important step is to talk to actual employees in a neutral dialogue if possible. I've hired several folks that have mentioned that you never know about a company until you've been there for a while. I agree but I don't think we have to be the one's to "try out" the company for a couple months to see if it's a right fit. That is not feasible and I prefer not to gamble with my career like that.
So talk to employees who have already done the "try out" for you. Ask them any questions that you feel would help you to know if the company is right for you. This is one of the best ways to research a company, if you can get the employee in an open and honest dialogue.
Playing off my last post, I decided to share an experience I had using LinkedIn to do background research. I had a scheduled in person sales call as a follow up from an event my company held out at the Miller Motorsports Park (What a great venue, by the way).
Before the appointment I googled this gentleman but could not find anything other than his LinkedIn profile. So I followed the link. Once on his profile I payed particularly close attention to his interests. He mentioned his interest in car restoration and racing, etc. There were a few other details I caught also.
When I arrived at his office I spent some time just chatting and let him know that I had reviewed his LinkedIn and saw his interests. We got to talking and connected on a deep personal level. We talked about his father who raced cars and his interest in cars. One of his restored cars broke down the other day and he had to take his wife's car. He was worried because his wife has cancer and goes to treatments. And on and on we got into deeper conversations. By that time he trusted me and shared with me all his competitive details that would take his business out if leaked.
This same idea will work in an interview. Find ways to connect with people on a deeper level and things will go more smoothly because they have a greater opportunity to trust you. Researching LinkedIn profiles can be a great tool for that reason.