Here we have a couple of things.
An annual survey for all employees with questions about what we think about the company, your boss, your job, salary, your insurance, etc. Its anonymous and we get the aggregate result at the end.
Alsos we have 2 evaluations of our boss to do each year. Is your supervisor honest? helpful? respectful? competent? etc, name 2 positives things about your boss, 2 negatives things about your boss, comments on your department, the company, etc. The boss is doing at the same time an evaluation about us. After we meet each other and talk about what we write down on the evaluation. Also he asks if we need formation or something else (a new software, monitors, computer, desk) and we need to rate on 10 our salary, our job appreciation, the company, how we see our future in the company, etc.
We also met with the boss of my boss every maybe 2 years. We talk about things more general about the company (what we like, what we dont like, ideas to improve company, etc.) and about my boss (things that I was not able to tell my boss).
And also each year, the president and owner pick maybe a dozen of employees ramdonly to get their thoughts about the company.