It can be difficult when you're a big corporate and no-one cares about the CEO sitting at the top of the ladder. You are still a small business, surely you speak to your staff on a personal level still? Next time you all get together for a meeting, tell them you will be sending them a form with a few simple questions, emphasise the fact that it's completely anonymous and make sure you point out what you want to accomplish which is essentially a better place for them to work. Everyone likes to believe that their opinion matters so this is your way of proving it to them.

Also, exit interviews are brilliant. When a member of staff quits, gets fired, comes to the end of their contract or whatever, hold a no strings attached exit interview and let them tell you everything they liked and didn't like about working for you and your company.